Optical waveguide and method of manufacturing the same

ABSTRACT

Some of the embodiments of this invention provide optical waveguides which achieve high use efficiency of core material and which are inexpensive. Some other embodiments of the invention provide methods of manufacturing such optical waveguides. An method of manufacturing an optical waveguide, according to the invention, comprises a step of forming a first clad by applying a resin on a substrate and curing the resin, a step of applying a core material between a recessed mold which has a recess having a shape identical to a shape of the core, and the first clad which is provided on the substrate, a step of curing the core material thus applied, thereby forming a core pattern having a shape corresponding to that of the recess, and a step of peeling the recessed mold from the core pattern and the first clad.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a Continuation Application of PCT Application No.PCT/JP03/11770, filed Sep. 16, 2003, which was not published under PCTArticle 21(2) in English.

[0002] This application is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2002-274670, filed Sep. 20,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates to an optical waveguide for use inoptical interconnections and the like, and a method of manufacturing theoptical waveguide.

[0005] 2. Description of the Related Art

[0006] Recent years have seen a remarkable progress of the opticalcommunications technology. It has been proved that the opticalcommunication is advantageous over the electric communication. As thesignal-processing speed in LSI and the like has increased, techniquesfor replacing electric signals with optical signals are being developed.It is expected that media for transmitting optical signals will bepolymer optical waveguides that have been developed in recently years.

[0007] The polymer optical waveguide can be formed to have a large area.Attempts have been made to apply the polymer optical waveguide tooptical interconnections of the order of 1 cm to 1 m. The polymeroptical waveguide may have, at one end, an optical-path changing mirror.This makes it possible to mount optical components on a surface justabove the optical-path changing mirror.

[0008] (Method of Manufacturing the Waveguide)

[0009] The polymer optical waveguide is manufactured, generally by amethod that uses dry etching as shown in FIG. 44 or by a method thatutilizes pattern exposure and development as shown in FIG. 45.

[0010] More specifically, in the method using dry etching, a first clad2 is formed on a substrate 50 and a core 1 is formed on the first clad2, as is illustrated at (a) in FIG. 44. As depicted at (b) in FIG. 44, asilicon-containing resist 51 is formed on a part of the core 1. As shownat (c) in FIG. 44, reactive ions 52 are applied to thesilicon-containing resist 51 and the core 1, thereby etching that partof the core 1 which is not covered with the silicon-containing resist51. As shown at (d) in FIG. 44, the silicon-containing resist 51 isremoved, forming a core 1 projecting upwards. As depicted at (e) in FIG.44, a second clad 3 is formed on the projecting core 1 and the firstclad 2.

[0011] In the method utilizing pattern exposure and development, a firstclad 2 is formed on a substrate 50 as shown at (a) in FIG. 45, and acore material 1′ is formed on the first clad 2 as illustrated at (b) inFIG. 45. As shown at (c) in FIG. 45, ultraviolet rays are applied to thecore material 1′ through a photo mask 35, thus curing a part of the corematerial 1′. As depicted at (d) in FIG. 45, that part of the corematerial 1′ which has not been cured is removed by means of development,forming a core 1 that projects upwards. As shown at (e) in FIG. 45, asecond clad 3 is formed on the projecting core 1 and the first clad 2.

[0012] The optical-path changing mirror is formed, as in most cases, bya mechanical process that uses a dicing saw as illustrated in FIG. 46.In the mechanical process using a dicing saw, a substrate 50 is preparedas shown at (a) in FIG. 46. The substrate 50 has clads 2 and 3 in whicha core 1 is embedded as is illustrated at (e) in FIG. 44 or (e) in FIG.45. As shown at (b) in FIG. 46, both ends of the core 1 are cutslantwise with a dicing blade 54. At the same time, the clads 2 and 3are cut slantwise with the dicing blade 54. As a result, both ends ofthe core 1 make total-reflecting mirrors 55 as depicted at (c) in FIG.46. At this time, an optical path is formed, through which signal light8 applied to one end of the core 1 passes until it emerges from theother end of the core 1.

[0013] The waveguide shown in FIG. 44 or FIG. 45 and the optical-pathchanging mirror shown in FIG. 46 are manufactured in separate processes.Inevitably, the manufacture of the system is complex and requires a highcost.

[0014] To manufacture the waveguide and the mirror at the same time, amethod using a mold has been devised (see, for example, Jpn. Pat. Appln.KOKAI Publication No. 2001-154049, pages 8 and 9, FIGS. 2 and 3). In themethod using a mold, the entire surface of a substrate that has a recessis coated with a core. The core is then removed from the substrate, butnot from the recess. A first clad is formed on the entire surface of thesubstrate, covering the core remaining in the recess. The core and thefirst clad are transferred onto a separate substrate. Thereafter, asecond clad is formed on the first clad.

[0015] In this method, the core applied to the entire surface of thesubstrate is removed, but not from the recess. The use efficiency ofcore material is therefore low. The cost of the method is high.

[0016] A method in which the core material is used at high efficiency isavailable (see, for example, Jpn. Pat. Appln. KOKAI Publication No.10-90544, page 7, FIGS. 1 to 5). This method uses a recessed mold thatis transparent to light and has a light-shielding film on its surface,but not over the recess. Hence, light is applied through the recessedmold, curing only the core pattern. However, the recessed mold, which ismade of resin, will likely be deformed by temperature deviation. Thecore pattern is inevitably deformed.

[0017] A similar technique is disclosed in W. J. Oh, M. S. Kim, H. H.Byum, J. W. Kim, K. S. Han, J. H. Oh, M. S. Kwon and S. Y. Shin,“Fabrication of Multimode Polymer Optical Waveguides by Using UV CurableResins and Transfer Molding Process,” Seventh Optoelectronics andCommunications Conference (OECC 2002), Technical Digest, pp. 534-535,July 2002. This technique uses light applied through a recessed mold,too; the thesis reads, “The PDMS mold is transparent to UV light (page534, right column, lines 11-12).” Since light is applied through therecessed mold, the mold made of resin is inevitably deformed.

[0018] (Mounting of an Optical Component)

[0019] The optical waveguide has a core on which an optical-pathchanging mirror is provided. An optical component, which is alight-emitting element or a light-receiving element, is mounted on thesurface of the optical waveguide lies on the optical axis of the mirror.

[0020] In most cases, the optical-path changing mirror is a planemirror. The plane mirror is disadvantageous in that the connectionefficiency is low when it guides light to the core from a light-emittingelement such as a vertical-cavity surface-emitting laser (VCSEL) or to alight-receiving element such as a photodiode (PD). The plane mirror isdisadvantageous also in that the displacement tolerance is small.

[0021] To connect the light-emitting element to the core, a convex lensis used, as in most cases, to convert the diverging light coming fromthe light-emitting element to focused light, which is applied to theoptical-path changing mirror. To connect the core to the light-receivingelement, a convex lens converts the light coming from the optical-pathchanging mirror to focused light, which is applied to the PD, in orderto increase the connection efficiency and the displacement tolerance forthe light-receiving element (see, for example, Jpn. Pat. Appln. KOKAIPublication No. 2001-185752).

[0022] In these methods, however, it is necessary to provide an opticalpath between the core and the convex lens, which is longer than thediameter of the core. This inevitably renders the entire system largeand complex. Further, the medium outside the lens must be one having asmall refractive index, and air is usually used. Thus, no highlyreliable structure, such as a transparent resin capsule, can be used.

[0023] Both the light-emitting element 40 and the light-receivingelement 41 may be provided near optical-path changing mirrors 4 and 6,as shown in FIG. 47, establishing the relation of the diameter of beamemitting area<the diameter of the core<the diameter of beam receivingarea. Thus, the light beam reaches the light-receiving element 41 beforeit greatly diverges. This renders it unnecessary to use the convex lens.This method is not so desirable, however. The light beam receiving areahas a large diameter, and the light-receiving element 41 can respond butslowly.

[0024] (Mounting of the Waveguides)

[0025] As FIG. 48 shows, straight waveguides, curved waveguides andinclined mirrors, each at the end of any waveguide, have been hithertoused (see, for example, p. 662, FIG. 8, Journal of the Society ofElectronic Data Communication, Vol. 84, No. 9, pp. 656-662, September2001). Straight waveguides are fundamental. A curved waveguide is usedto change the position or orientation of a straight waveguide. Inclinemirrors are used to connect waveguides to surface-emitting elements orlight-emitting elements (hereinafter, referred to as “externalelements”).

[0026] Many cores are required in complex circuit. In a complex circuit,it is difficult to amount straight waveguides and curved waveguides inhigh density. This is because each curved waveguide cannot have a smallradius of curvature; the smaller the radius of curvature, the greaterthe loss of light. Since the curved waveguides need to have a largeradius of curvature, a large area is required to change the direction ofthe optical path. It is therefore difficult to increase the density atwhich the waveguides may be mounted.

[0027] Further, in complicated circuits, the setting must be repeatedmany times to process mirrors by laser cutting.

[0028] In summary, any structure comprising straight waveguides, curvedwaveguides and inclined mirrors, each provided at the end of eachwaveguide, is not considered to be fit for providing cores that connectmany points at various positions.

[0029] (Bonding to Another Substrate)

[0030] How an optical waveguide 7 is made in the form of a film andbonded to another substrate will be described below.

[0031] How a film, or optical waveguide 7, is formed as is illustratedin at (a) to (f) in FIG. 49. As shown at (a) in FIG. 49, a first clad 2is formed on a substrate 20. As depicted at (b) in FIG. 49, alignmentmarks 79 are formed on selected parts of the first clad 2. Then, asshown at (c) in FIG. 49, a core 1 is formed on the first clad 2, notoverlapping the alignment marks 70. At (c) in FIG. 47, the core 1 isdepicted as if overlapping the alignment marks 70. However, the core 1is displaced from the marks 70 in the direction perpendicular to theplane of the drawing. As shown at (d) in FIG. 49, a second clad 3 isformed on the core 1 and the first clad 2. The waveguide 7 is thusprovided on the substrate 20. Thereafter, as shown at (e) in FIG. 49,inclined, total-reflection mirrors 55 are formed at the ends of the core1. The substrate 20 is peeled off the optical waveguide 7. The opticalwaveguide 7, shaped like a film as depicted at (f) in FIG. 49, istherefore manufactured.

[0032] Next, as shown at (g) in FIG. 49, the optical waveguide 7 isbonded with adhesive 62 to another substrate (e.g., a wiring board) 60,with one alignment mark 70 aligned with alignment marks 61 that areprovided on the substrate 60. This completes the bonding of the opticalwaveguide 7 to the other substrate 60.

[0033] This bonded structure can hardly be controlled, however, in thethickness of the adhesive layer 62. The distance between the opticalwaveguide 7 and the other substrate 60 may change in accordance with thethickness of the adhesive layer 62. Further, the precision ofpositioning the waveguide 7 with respect to the substrate 60 is lowbecause the alignment mark 70 is spaced apart from the alignment marks61 by a long distance.

BRIEF SUMMARY OF THE INVENTION

[0034] An object of this invention is to provide a method ofmanufacturing an optical waveguide which is inexpensive and in which thecore is used at high efficiency and scarcely deformed.

[0035] Another object of the invention is to provide an opticalwaveguide that excels in mirror-connection efficiency, which has a largetolerance for element displacement and which is simple in structure andinexpensive.

[0036] Still another object of the invention is to provide an opticalwaveguide in which a core can be easily formed to connect many givenpoints.

[0037] A further object of the present invention is to provide anoptical waveguide, which can be spaced from, and positioned with respectto, another substrate and which is therefore fit to be bonded to thesubstrate.

[0038] According to a first aspect of this invention, there is provideda method of manufacturing an optical waveguide that has a core andclads. The method comprises: a step of forming a first clad by applyinga resin on a substrate and curing the resin; a step of applying a corematerial between a recessed mold having a recess identical to a shape ofthe core and the first clad provided on the substrate; a step of curingthe core material thus applied, thereby forming a core pattern having ashape identical to that of the recess; and a step of peeling therecessed mold from the core pattern and the first clad.

[0039] Since the core material is pressed into the recess of the mold,its use efficiency is high. Since no light is applied through therecessed mold, the core is hardly deformed. Therefore, the method canmanufacture the optical waveguide at low cost.

[0040] According to a second aspect of this invention, there is providedan optical waveguide in which a core is interposed between clads. Theoptical waveguide comprises a concave mirror which is provided at oneend of the core and which guides signal light applied in a directionperpendicular to the waveguide, into the core. The concave mirror has afocal distance that is substantially equal to a distance from a centerpoint of the concave mirror to a light-emitting point of alight-emitting element that generates the signal light.

[0041] Having such a concave mirror, the optical waveguide excels inmirror-connection efficiency, can have a large tolerance for elementdisplacement, and is simple in structure and inexpensive.

[0042] According to a third aspect of this invention, there is providedan optical waveguide that has a plurality of cores interposed betweenclads. The first core comprises a plurality of straight waveguidesextending in at least two directions and connected to each other with anin-plane mirror. Another core comprises a straight waveguide extendingin a direction that is substantially identical to one of the directionsin which the straight waveguides included in the first core extend.

[0043] The use of the in-plane mirror can reduce the area required tochange the direction of the optical path. Further, the cores arestandardized to have a straight waveguide that may extend in the twodirections. This reduces the number of times the setting of the lasercutting process should be repeated. Hence, in the optical waveguide,each core can be easily formed to connect many given points.

[0044] According to a fourth aspect of this invention, there is providedan optical waveguide that can be bonded to another substrate. Thisoptical waveguide comprises: a first clad; a core formed on a part ofthe first clad; a base formed on a part of the first clad and having atop at a level equal to or higher than a top of the core; an alignmentmark formed on the top of the base; and a second clad formed on thefirst clad and covering the core.

[0045] Having a base and an alignment mark, this optical waveguide canbe precisely positioned with respect to another substrate, at a desireddistance from the substrate. Thus, the optical waveguide is fit to bebonded to the substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0046]FIG. 1 is sectional views explaining a method of manufacturing anoptical waveguide according to a first embodiment of the presentinvention;

[0047]FIGS. 2 and 3 are sectional views explaining a modification of themethod of manufacturing the first embodiment;

[0048]FIG. 4 is sectional views and perspective views, explaining amethod of manufacturing a recessed mold for use in the first embodiment;

[0049]FIGS. 5 and 6 are perspective views of two types of opticalwaveguides that may be used in the first embodiment;

[0050]FIGS. 7 and 8 are schematic diagrams showing the angles at whichpress rolls may be moved in the first embodiment;

[0051]FIGS. 9A and 9B are perspective views of a type of a recessed moldthat may be used to manufacture the first embodiment;

[0052]FIGS. 10 and 11 are sectional views explaining a modification ofthe method of manufacturing the first embodiment;

[0053]FIG. 12 is sectional views showing a method of manufacturing anoptical waveguide according to a second embodiment of the presentinvention;

[0054] FIGS. 13 to 15 are sectional views illustrating a modification ofthe method of manufacturing the optical waveguide according to thesecond embodiment;

[0055]FIG. 16 is a sectional view of the core pattern provided in thesecond embodiment;

[0056]FIG. 17 is a diagram explaining how the contact angle changes asthe oxygen-plasma process proceeds in manufacturing the secondembodiment;

[0057]FIG. 18 is sectional views showing a method of manufacturing anoptical waveguide prepared for comparison with the optical waveguideaccording to the second embodiment;

[0058]FIGS. 19 and 20 are sectional views schematically illustrating anoptical waveguide according to a third embodiment of the presentinvention;

[0059]FIG. 21 is sectional views depicting a method of manufacturing theoptical waveguide according to the third embodiment;

[0060] FIGS. 22 to 25 are perspective views explaining a method offorming a recessed surface in the third embodiment;

[0061]FIG. 26 is a perspective view illustrating an optical waveguideaccording to a fourth embodiment of the invention;

[0062]FIGS. 27A and 27B and FIGS. 28A and 28B show various types ofin-plane mirrors and various types of inclined mirrors, which may beused in the fourth embodiment;

[0063]FIG. 29 is a diagram for explaining a method of manufacturing theoptical waveguide according to the fourth embodiment;

[0064]FIGS. 30 and 31 are perspective views showing the shape of thein-plane mirror used in the fourth embodiment and a method ofmanufacturing the in-plane mirror;

[0065]FIG. 32 is perspective views depicting the shape of an ordinaryin-plane mirror and a method of forming the ordinary in-plane mirror;

[0066]FIGS. 33 and 34 are perspective views illustrating the shape of aninclined mirror provided in the fourth embodiment and explaining amethod of forming the inclined mirror;

[0067]FIG. 35 is perspective view showing the shape of an ordinaryinclined mirror and a method of forming the ordinary inclined mirror;

[0068] FIGS. 36 to 43 are sectional views explaining a method ofmanufacturing an optical waveguide according to a fifth embodiment ofthe invention;

[0069]FIG. 44 is sectional views showing a conventional method ofmanufacturing an optical waveguide;

[0070]FIG. 45 is sectional views illustrating another conventionalmethod of manufacturing an optical waveguide;

[0071]FIG. 46 is sectional views showing a conventional method ofmanufacturing a mirror;

[0072]FIG. 47 is a sectional view of a conventional optical waveguide;

[0073]FIG. 48 is a perspective view of an conventional opticalwaveguide; and

[0074]FIG. 49 is sectional views showing a conventional method ofmanufacturing an optical waveguide.

DETAILED DESCRIPTION OF THE INVENTION

[0075] Modes and embodiments of this invention will be described indetail, with reference to the accompanying drawings. The embodiments canbe combined one with any other. The first and second embodiments relatemainly to methods of manufacturing optical waveguides. The thirdembodiment is concerned mainly to the mounting of external elements. Thefourth embodiment relates chiefly to the forming of a complex circuit.The fifth embodiment relates mainly to the bonding of optical waveguidesto another substrate.

[0076] (First Embodiment)

[0077]FIG. 1 is sectional views explaining a method of manufacturing anoptical waveguide according to a first embodiment of the presentinvention.

[0078] First, a recessed mold 10 is prepared. As shown at (a) in FIG. 1,the mold 10 has a recess having the shape of a core pattern to beformed. At least the surface regions of the mold 10 are made of siliconeor fluororesin. Meanwhile, a substrate 20 is prepared, and a first clad2 is formed on the substrate 20 and cured, as is illustrated at (b) inFIG. 1.

[0079] As shown at (c) in FIG. 1, a core material 1′ is laid between therecessed mold 10 and the substrate 20. Rolls 11, for example, press thecore material 1′, recessed mold 10 and substrate 29 together. The coremember 1′ is thereby pressed into the recess of the mold 10.

[0080] Then, as depicted at (d) in FIG. 1, ultraviolet rays are appliedto the substrate 20, curing the core material 1′. A core pattern 1 isthereby formed.

[0081] The recessed mold 10 is removed. As a result, the core pattern 1is mounted on the first clad 2 as shown at (e) in FIG. 1.

[0082] This structure can function as a waveguide, because air serves asupper clad. Nonetheless, it is desired that the core pattern 1 and thefirst clad 2 be covered with a second clad 3 as shown at (f) in FIG. 1,in order to form a waveguide. If the waveguide need not have mirrors,its input and output ends are bare, as is illustrated at (g) in FIG. 1.

[0083] The waveguide 7 may be formed by using a mold 10 having a recessthat has mirror-equivalent surfaces 4′ inclined at 45° as shown in FIGS.2 and 3. This recessed mold 10 has been made as will be describe later,with reference to FIG. 4(a-e). The recessed mold 10 is not limited toone that has inclined mirror-equivalent surfaces 4′ at ends as shown at(f) in FIG. 4. Rather, it may be one that has not only inclinedmirror-equivalent surfaces 4′, but also a surface 5′ equivalent to anin-plane mirror, at the middle part of the recess as is illustrated at(g) in FIG. 4.

[0084] The mold 10 having surfaces 4′ equivalent to inclined mirrors, asshown at (f) in FIG. 4 may be used to form the waveguide 7. In thiscase, inclined mirror surfaces 4 for changing the optical path can beformed at the ends of the core pattern 1 as is illustrated in FIGS. 2, 3and 5, at the same time the core pattern 1 is formed.

[0085] The mold 10 having surface 5′ equivalent to in-plane mirror, asshown at (g) in FIG. 4, may be used instead. In this case, in-planemirror surface 5 for changing the optical path can be formed on the corepattern 1 at the same time the core pattern 1 is formed.

[0086] A method of producing the recessed mold 10 will be explained.

[0087] First, a projection having the shape of a core pattern to produceis formed on a substrate 31 as illustrated at (a) to (c) in FIG. 4. Theprojection can be formed easily, by first coating the substrate 31 witha photosensitive resin layer 32 (e.g., a photo-resist), then exposingthe layer 32 to light with photomask and finally developing the layer32.

[0088] Mirror-equivalent surfaces 4′ inclined at 45° for changing theoptical path can be formed at the ends of the core pattern. Morespecifically, the surfaces 4′ equivalent to inclined mirrors areprovided by a laser cutting process in which a laser beam 33 isobliquely applied as shown at (b) in FIG. 4. The laser process uses KrFexcimer laser, an ArF excimer laser, a femto-second laser, a UV-YAGlaser or the like, which emits a beam consisting of high-energy photons,having a wavelength in the ultraviolet region and capable of cuttingmolecules. A surface 5′ equivalent to an in-plane mirror for changingthe optical path can be provided at the middle part of the core pattern.The surfaces 5′ equivalent to in-plane mirrors may be formed either byexposure and development at the same time or by laser cutting after thecore pattern is made.

[0089] Thus, a projecting mold 30 having a projection with two surfaces4′ equivalent to inclined mirrors at the ends, respectively, is formedas shown at (c) in FIG. 4.

[0090] Next, silicone or fluororesin, in the form of liquid, is pouredonto the projecting mold as shown at (d) in FIG. 4. The silicone orfluororesin is cured at room temperature or by heating to provide arecessed mold 10.

[0091] After the silicone or fluororesin is cured, the projecting mold30 is removed. As a result, a recessed mold 10 is made as is illustratedat (e) in FIG. 4.

[0092] The recessed mold 10 has a recess that may have mirror-equivalentsurfaces 4's shown at (f) in FIG. 4 or mirror-equivalent surface 5′ asdepicted at (g) in FIG. 4.

[0093] Description shall be reverted to the manufacture of thewaveguide. The waveguide 7 may be made by using the recessed mold 10having surfaces 4′ equivalent to inclined mirrors, as shown in FIG. 2.If this is the case, it is desirable to provide reflecting films 6 onthe mirror surfaces 4 and 5 of the core pattern 1 as illustrated at (f)in FIG. 2. The reflecting films 6 are preferably metal films (Al, Ag, Cuor the like). Each film 6 may be a multi-layer film. The reflectingfilms 6 can be formed by various methods, such as vapor depositionthrough mask, etching process or lift-off process. (The etching processis performed after a film is formed on all exposed surfaces of the corepattern 1.)

[0094] Alternatively, the reflecting films 6 may be first formed on themirror-equivalent surfaces 4′ and 5′ of the recessed mold 10 and thentransferred to the mirror-equivalent surfaces 4 and 5 of the corepattern 1 as the mold 10 is removed from the core pattern 1.

[0095] Preferably, the clads 2 and 3 are made of epoxy resin. To curethe clads 2 and 3, ultraviolet rays or heat is applied to the clads 2and 3. Instead, both ultraviolet rays and heat can be applied to theclads 2 and 3.

[0096] To fill the core material 1′, press-rolling is performed asdesirable process. More precisely, the rolls 11 are rotated and movedover the core material 1′, while applying a pressure on the corematerial 1′. The press rolling can therefore press the core material 1′into the recess of the mold 10, which has the same shaped as a corepattern to be made. The process can remove bubbles from the corematerial 1′. In FIGS. 1 to 3, the recessed mold 10 lies beneath thesubstrate 20. Instead, the substrate 20 may be positioned beneath therecessed mold 10.

[0097] As FIG. 7 shows, it is desired the angle θ between the straightpart of the waveguide and the direction 11 a in which the press rollsmove should be as small as possible. If this angle is equal to orsmaller than 45°, the core material 1′ can be pressed into the recess asis desired. As FIG. 6 depicts, the straight waveguide may have two partsextending in two directions that are at right angles to each other. Inthis case, as shown in FIG. 8, the two parts of the waveguides areinclined at about 45° to the direction 11 a in which the press rolls aremoved. Then, the core material 1′ can be pressed well into the recess ofthe mold 10.

[0098] The core material 1′ should better be made of epoxy resin oracrylic resin. Ultraviolet rays or heat, or both may be applied to thecore to cure the same. Application of ultraviolet rays is particularlyimportant because it can minimize the temperature change to achieve ahigh precision of size.

[0099] To enhance the size precision, it is necessary to suppress theshrinking of the recessed mold 10 in the curing process of mold. Inorder to suppress the mold shrinking, the recessed mold 10 needs to havea backplate 15 as is illustrated in FIG. 9A. The backplate 15 may bemade of material having a smaller thermal expansion coefficient than theresin 34 that is the material of the recessed mold 10. That is, thebackplate 15 may be made of inorganic material such as metal. Then, thechange in size can also be controlled, which results from thetemperature changes that occur as the core is cured. It would be thebest if the backplate 15 were made of material that has the same heatexpansion coefficient as the substrate 20 that has the clad 2.

[0100] Since the recessed mold 10 described above is used, it isimportant to apply ultraviolet rays 12 to the core material 1′ throughthe substrate 20. This is because ultraviolet rays can hardly passthrough the backplate 15, which is made of metal or the like. Thus, thesubstrate 20 should be made of material that is transparent toultraviolet rays. Preferred as material transparent to ultraviolet raysis, for example, glass.

[0101] When the core material 1′ is interposed, a thin core 13 remainson the entire surface, as shown at (a) in FIG. 10. The core 13 can bemade as thin as about 1 μm by means of optimization. Being so thin, thecore 13 scarcely makes a problem to the optical waveguide. If the corepattern 1 is very close to an adjacent one, however, the core 13 willcause a cross talk.

[0102] In view of this, the core 13 is removed as shown at (b) in FIG.10, after the recessed mold 10 is peeled off. The core 13 can be removedby subjecting the entire structure to, for example, oxygen-plasmaprocess. Alternatively, the core 13 can be removed by lightly treatingthe entire structure with chemicals. Then, the cross talk can be reducedeven if the core patterns 1 are arranged in short pitches. Since thecore 13 remains in the form of a layer as thin as 1 μm, it can beremoved in a short time, making no problems in the manufacture of theoptical waveguide.

[0103] As shown at (b) in FIG. 11, a separation layer 14 may be formedon the substrate 20 before the waveguide 7 is manufactured. After thewaveguide 7 is manufactured, the separation layer 14 is removed from theclad 2, thus removing the substrate 20. Thus, the waveguide 7 can be anindividual film as is shown at (i) in FIG. 11.

[0104] Ultraviolet rays may be applied through the substrate 20 to curethe core. Then, it is desired that the separation layer 14 istransparent to ultraviolet rays 12. The separation layer 14 can be athin photoresist or a water-soluble adhesive layer.

[0105] Examples 1 to 9 of the first embodiment described above will bedescribed. Examples 1, 4 and 9 are concerned with the recessed mold.Examples 2, 3 and 5 are related to the optical waveguide. Examples 6 and7 are related to the press rolling and the orientation of the waveguide.Example 8 is concerned with the technique of providing the waveguide inthe form of a film. These examples will be described, one by one.

EXAMPLE 1

[0106] [Recessed Mold 1]

[0107] Example 1 of the first embodiment will be explained, withreference to FIG. 4. First, a dry film resist was laminated to thesubstrate 31 (made of glass) as is illustrated at (a) in FIG. 4. Theresist was exposed to light through photomask and developed. Aprojecting pattern, or photosensitive-resin pattern 32, was therebyformed. The pattern 32 was shaped like a core and its height and widthwere 40 μm.

[0108] Next, as shown at (b) in FIG. 4, a KrF excimer laser applied as alaser beam 33 obliquely, thus forming mirror surfaces 4′. A projectingmold was formed as illustrated at (c) in FIG. 4.

[0109] Then, silicone resin 34 in liquid state was applied to theprojecting mold and cured as shown at (d) in FIG. 4. Thereafter, theprojecting mold was removed from the silicon resin layer 34, forming arecessed mold 10 as shown at (e) in FIG. 4.

EXAMPLE 2

[0110] [Waveguide 1]

[0111] Example 2 of the first embodiment will be described, withreference to FIG. 2. At first, a recessed mold 10 (made of siliconeresin) made in Example 1 is prepared as shown at (a) in FIG. 2.

[0112] Next, a substrate 20 (made of glass) is prepared.Ultraviolet-curable epoxy resin was applied, as clad material, to thesubstrate 20 by means of spin coating. Ultraviolet rays were applied tothe entire surface of the substrate at intensity of 4 J/cm², curing theclad material. A first clad 2 having a thickness of 30 μm was therebyformed on the substrate 20, as is illustrated at (b) in FIG. 2.

[0113] Then, ultraviolet-curable epoxy resin was dripped, as corematerial 1′ onto the recessed mold 10. As shown at (c) in FIG. 2, thesubstrate 20 having the clad 2 was laid on the recessed mold 10 and waspassed, together with the mold 10, through a roll laminator.

[0114] The rolls pressed the recessed mold 10 and the substrate 20having the clad 2, pushing the core material 1′ into the recess of themold 10.

[0115] As depicted at (d) in FIG. 2, ultraviolet rays 12 are appliedthrough the substrate 20 at intensity of 8 J/cm². The core material 1′was thereby cured, forming a core pattern 1.

[0116] As shown at (e) in FIG. 2, the recessed mold 10 was removed.Using a mask, Al was vapor-deposited as shown at (f) in FIG. 2, thusforming reflecting films 6 on the inclined mirror surfaces 4 of the corepattern 1.

[0117] Further, ultraviolet-curable epoxy resin was applied, forming asecond clad 3. Ultraviolet rays were applied at intensity of 4 J/cm². Asa result, a waveguide 7 was formed as illustrated at (g) in FIG. 2.

Example 3

[0118] [Optical Waveguide 2]

[0119] Example 3 of the first embodiment will be described, withreference to FIG. 3. First, a recessed mold 10 (made of silicone resin)made in Example 1 is prepared as shown at (a) in FIG. 3. Using a mask,Al was vapor-deposited as shown at (b) in FIG. 3. Reflecting films 6were thereby formed on the inclined mirror-equivalent surfaces 4′. Then,a core pattern 1 was formed on the first clad 2 as shown at (c) to (e)in FIG. 3, in the same way as depicted at (b) to (d) in FIG. 2.Nonetheless, the core material 1′ was one made of ultraviolet-curableacrylic resin.

[0120] Next, the Al films, i.e., reflecting films 6, were transferred tothe inclined mirror surfaces 4 of the core pattern 1 as shown at (f) inFIG. 3, when the recessed mold 10 was removed. Then, a second clad 3 wasformed in the same way as already explained, as illustrated at (g) inFIG. 3. As a result, a waveguide 7 was manufactured.

Example 4

[0121] [Recessed Mold 2]

[0122] Example 4 of the first embodiment will be described, withreference to FIG. 4. First, ultraviolet-curable epoxy resin is appliedon a substrate 31 (made of glass). The resultant structure was exposedto light through photomask and developed with a solvent. A projectingpattern 32 made of photosensitive resin was thereby formed as isillustrated at (a) in FIG. 4.

[0123] This pattern's height and width were 40 μm. The pattern was notonly straight line but had a surface 5′ (not shown) equivalent to anin-plane mirror, too.

[0124] Next, laser beams 33 emitted from a femto-second laser wereobliquely applied, to the pattern 32 made of photosensitive resin,forming surfaces equivalent to inclined mirrors, as shown at (b) in FIG.4. As a result, a projecting mold 30 was obtained as illustrated at (c)in FIG. 4.

[0125] As depicted at (d) in FIG. 4, fluororesin 34 was applied on theprojecting mold 30 and cured with heat. The resultant fluororesin layer34 was removed from the projecting mold 30. A recessed mold 10 made offluororesin was thereby made as is shown at (e) in FIG. 4.

Example 5

[0126] [Optical Waveguide 3]

[0127] Example 5 of the first embodiment will be described, withreference to FIG. 2. Example 5 is a waveguide 7 that was made as shownat (b) to (g) in FIG. 2, first by preparing a recessed mold 10 (made offluororesin) produced in Example 4 as is illustrated at (a) in FIG. 2.

Example 6

[0128] [Press-Rolling and Orientation 1 of Waveguide]

[0129] A recessed mold 10 having a straight core pattern as shown at (f)in FIG. 4 was used.

[0130] Test was repeated, changing the angle θ between the orientationof the straight recess of the recessed mold 10 and the direction inwhich the mold 10 was moved through the roll laminator, as isillustrated in FIG. 7 and at (c) in FIG. 2.

[0131] The core material 1′ could be pressed into the recess as isdesired, when the angle θ was 0°, 30° and 45°. When the angle θ was 60°,some bubbles were observed in the core material 1′. When the angle θ was90°, many bubbles were observed in the core material 1′.

Example 7

[0132] [Press-Rolling and Orientation 2 of Waveguide]

[0133] A recessed mold 10 that had two straight grooves extending atright angles to each other and a surface 5′ equivalent to an in-planemirror, as is illustrated at (g) in FIG. 4, was used.

[0134] As shown at (c) in FIG. 2, press rolling was performed such thatthe angle between the direction in which the roll laminator was movedand the directions in which the straight grooves of the recessed mold 10was almost 45°. As a result, the core material 1′ was pressed into therecess as is desired.

Example 8

[0135] [Making the Waveguide as an individual Film]

[0136] What is shown at (a) in FIG. 11 is identical to what is shown at(a) in FIG. 2. As depicted at (b) in FIG. 11, a positive resist wasapplied to a substrate 20, forming a separation layer 14 having athickness of 1 μm. After the resultant structure was baked, a waveguidewas made as shown at (c) to (h) in FIG. 11, in the same way as inExample 2.

[0137] The waveguide thus produced was immersed in a peeling liquid,dissolving the separation layer 14 as is illustrated at (i) in FIG. 11.Thus, the waveguide was shaped as an individual a film.

[0138] Infrared rays having wavelength of 0.85 μm were applied throughoptical fibers to one inclined mirror surface 4. The infrared rays wereobserved to emerge from the other inclined mirror surface 4.

Example 9

[0139] [Recessed Mold 3]

[0140] At first, a projecting mold 30 was formed in the same manner asin Example 1. Next, silicone resin in liquid state was poured onto theprojecting mold 30, and a stainless steel plate was laid, as backplate15, on the silicone layer 34.

[0141] The silicone layer 34 was cured at room temperature in thiscondition. Then, the projecting mold 30 was peeled off. A recessed mold10 was thereby made as is illustrated in FIG. 9A.

[0142] Using the recessed mold 10 having the backplate 15, a waveguide 7was manufactured in the same way as in Example 2. This waveguide 7 had acore pattern 1 that had almost the same size as the mask pattern.

[0143] Meanwhile, a recessed mold 10 having no backplate was used, thusmaking a core pattern 1 in the same way as in Example 2. This corepattern was smaller by 0.5% than the mask pattern.

[0144] As described above, the first embodiment and Examples 1 to 9thereof are advantageous in the following respects.

[0145] First, the deformation of the core pattern 1 can be suppressedbecause the recessed mold 10 is made of silicone or fluororesin 34.Further, since the core material 1′ has been pressed into the recess ofthe mold 10, the use efficiency of the core member is high, making itpossible to manufacture the waveguide at low cost.

[0146] Secondly, the mirror surfaces 4 and 5 can be provided at the sametime the core pattern 1 is formed, because the recessed mold 10 hasmirror-equivalent surfaces 4′ and 5′.

[0147] Thirdly, the core 13 remaining on the entire surface after therecessed mold 10 is peeled off can be easily removed, because it isthin.

[0148] (Second Embodiment)

[0149]FIG. 12 is sectional views that illustrate a method ofmanufacturing an optical waveguide according to a second embodiment ofthis invention. First, a recessed mold 10 is prepared as shown at (a) inFIG. 12.

[0150] The recessed mold 10 serves as a mold for forming the opticalwaveguide. The recessed mold 10 has a patterned recess. Not only thecore pattern of the optical waveguide, but also mirror-equivalent parts,a diffraction grating or optical circuits such as a branch or an arrayedwaveguide grating can be pressed into the patterned recess.

[0151] Preferably, the recessed mold 10 is made of silicone resin. Thisis because silicone resin is soft, rendering it easy to put the corepattern to a substrate having a clad and to peel the mold from thesubstrate, and not damaging the core pattern.

[0152] The recessed mold 10 may be made of silicone resin in itsentirely. Preferably, at least its surface region having the patternedrecess is made of silicone resin.

[0153] Next, a surface treatment is performed on the recessed mold 10 asshown at (b) in FIG. 12. The surface treatment can enhance the affinityof the recessed mold 10 for the core material 1′. To be more specific,the angle at which the core material 1′ contacts the recessed mold 10 isset at 45° or less. The core material 1′ can therefore be pressed intothe recess reliably. As the surface treatment, an oxygen-plasma processis preferable.

[0154] Then, as shown at (c) to (d) in FIG. 12, the core material 1′ isfilled in only the patterned recess made in the substrate. It ispreferred that the core material 1′ be made of, for example, epoxyresin. Particularly, ultraviolet-curable epoxy resin is desirable.

[0155] The core material 1′ can be filled in the recess by variousmethods. For example, a spatula 46 may be used to scrape off theexcessive part of the core material. After that, ultraviolet rays areapplied, curing the core material 1′. A core pattern 1 is therebyobtained.

[0156] A substrate 20 is prepared as depicted at (e) in FIG. 12. Cladmaterial 2′ is applied to the entire surface of the substrate 20. Asshown at (f) in FIG. 12, the recessed mold 10 having the core pattern 1is laid on the substrate 20 to which the clad material 2′ has beenapplied. In this condition, ultraviolet rays are applied, curing theclad material 2′ and forming a first clad 2. Thereafter, the recessedmold 10 is peeled off, thus transferring the core pattern 1 to thesubstrate 20.

[0157] It is desired that the clad material 2′ is ultraviolet-curableepoxy resin. The core material 1′ and the clad material 2′ may be curedby methods other than application of ultraviolet rays.

[0158] The optical-path changing mirrors are metal mirrors 4 and 6formed by depositing metal on the inclined surfaces 4 of the corepattern 1 as is sown at (g) in FIG. 12. To deposit the metal exclusivelyon the inclined surfaces, the vapor deposition through mask or thelift-off method may be employed. The optical-path changing mirrors arenot limited to the type that change an optical path to one that extendsperpendicular to the optical waveguide layer. They may be of theconfiguration shown in FIG. 6, which changes an optical path to one thatextends at any angle in the plane of the optical waveguide layer.

[0159] Next, as depicted at (h) in FIG. 12, clad material 3′ is appliedto the entire surface of the resultant structure. The clad material 3′is cured, forming a second clad 3. A single-layer optical waveguide 7 isthereby manufactured. The second clad 3 may not be formed. In this case,air is used as a clad.

[0160] As FIG. 13 illustrates, a core pattern 1A may be formed inanother recessed pattern 10A and then be transferred, thereby providinga multi-layer optical waveguide 7. What is shown at (h) in FIG. 13corresponds to what is depicted at (h) in FIG. 12.

[0161] To form the multi-layer optical waveguide 7 or to transfer asingle- or multi-layer optical waveguide to another substrate (e.g.,electric wiring board), it is desirable to use alignment marks (notshown) made on the substrate 20 or the first clad 2.

[0162] The single- or multi-layer optical waveguide may be used in theform of an individual film. In this case, it is desired that aseparation layer (not shown) be interposed between the substrate 20 andthe clad 2. After the optical waveguide has been made, the separationlayer is removed from the clad 2, thus providing the optical waveguidein the form of a film. It is also desired that the substrate 20 and theseparation layer, (or the recessed mold 10,) be transparent toultraviolet rays.

[0163] To manufacture the recessed mold 10, a projecting mold 30 may befirst made, silicone resin 34 or the like may then be applied to themold 30, curing, and the mold 30 may be removed from the layer.

[0164] The core pattern may, as in most cases, have an aspect ratio(height/width) of about 1. In this case, the mirror that changes theoptical path to one extending perpendicular to the optical waveguidelayer looks almost square when viewed from above. It means theclearances of component alignment are almost same in both x- andy-directions. Nonetheless, the waveguide can perform its function evenif the aspect ratio of the core pattern is not 1. In fact, the inventorshereof have confirmed that waveguides work well though their corepatterns have an aspect ratio ranging from 0.27 to 2.

[0165] As described above, the core material 1′ is filled in thepatterned recess only, cured and laid on the substrate 20 having a rawclad. Instead, as shown in FIG. 14, the core material 1′ may be clampedbetween the recessed mold 10 and the substrate 20 having a cured clad,thereby to manufacture a waveguide. More specifically, a recessed mold10 is prepared as shown at (a) in FIG. 14 and surface-treated asdepicted at (b) in FIG. 14. Next, a substrate 20 having a clad isprepared as depicted at (c) in FIG. 14. Then, core material 1′ issandwiched between the recessed mold 10 and the substrate 20, as isillustrated at (d) in FIG. 14.

[0166] As shown at (e) in FIG. 14, the core material 1′ is cured by, forexample, applying ultraviolet rays through the substrate 20 and/or therecessed mold 10. A core pattern 1 is thereby formed. The recessed mold10 is removed, and the core pattern 1 is transferred to the substrate20. Then, as shown at (f) in FIG. 14, metal is vapor-deposited on theinclined surfaces of the core pattern 1, forming metal mirrors 4 and 6.A second clad 3 may be formed, covering the core pattern 1 and the firstclad 2 as in most cases, as is illustrated at (g) in FIG. 14. In thiscase, too, a surface treatment can provide a reliable core. This methodcan manufacture multi-layer waveguides, too.

[0167] Not only the recessed mold 10, but also a projecting mold 16 canbe used as will be described with reference to FIG. 15. First, a clad 2having a patterned recess is made by using the projecting mold 16 thathas been surface-treated, as is illustrated at (a) to (e) in FIG. 15.Next, metal mirrors 4 and 6 are formed, a core 1 is then embedded andcovered with a clad 3, as is depicted at (f) to (i) in FIG. 15. Thismethod can manufacture a waveguide, too.

[0168] A method of manufacturing an optical waveguide according to thisinvention will be described in detail, with reference to Examples 10 to13.

EXAMPLE 10

[0169] [Preparation of the Mold]

[0170] A recessed mold 10 was made as shown in FIG. 4. The mold 10 had aplurality of grooves that define the shape of an optical waveguide tomanufacture. Each of the grooves had a height of 40 μm and a widthranging m to 150 μm.

[0171] [Manufacturing of Optical Waveguide 1]

[0172] How an optical waveguide was manufactured will be explained, withreference to FIGS. 12 and 16. At first, a recessed mold 10 (made ofsilicone resin) was prepared as shown at (a) in FIG. 12. Next, anoxygen-plasma process was performed on a substrate having a patternedrecess, as is illustrated at (b) in FIG. 12. The apparatus employed tocarry out the process was OPM-SQ600 (model number) manufactured by TokyoOhka Kogyo Co., Ltd. In the process, oxygen was applied for 2 minutes atflow rate of 100 SCCM, pressure of 60 Pa and plasma power of 100 W.

[0173] Then, ultraviolet-curable epoxy resin was applied to the entiresurface of the mold 10 in order to form core 1. All epoxy resin, butthat part filled in the recess, was scraped with a spatula 46.Ultraviolet rays were applied to the entire surface, curing the corematerial 1′. Core patterns 1 are thereby formed.

[0174] The core patterns 1 formed in grooves were continuous and hadcore widths ranging from 20 μm to 150 μm as is desired, shown in FIG.16.

[0175] Meanwhile, a substrate 20 (made of glass) was prepared as shownat (e) in FIG. 12. Ultraviolet-curable epoxy resin was applied, as cladmaterial 2′, to the entire surface of the substrate 20 by mean of spincoating.

[0176] As shown at (f) in FIG. 12, the mold 10 and the clad 2 are laidone on the other. Ultraviolet rays are applied through the substrate 20,thus bonding the core pattern 1′ and the clad material 2′ to each other.At the same time, the clad material 2′ was cured, forming a clad 2.

[0177] The recessed mold 10 is peeled off as is depicted at (g) in FIG.12. Then, Al is deposited on the inclined surfaces by means ofdeposition through mask, thereby forming mirrors 4 and 6. Further, asshown at (h) in FIG. 12, ultraviolet-curable epoxy resin, or cladmaterial 3′, was applied to the entire surface of the resultantstructure. Ultraviolet rays were then applied, thus manufacturing anoptical waveguide 7.

EXAMPLE 11

[0178] [Manufacturing of Optical Waveguide 2]

[0179] The contact angle of the core material to the mold was measured,while maintaining the conditions of oxygen-plasma process, i.e., theoxygen flow rate at 100 SCCM and the pressure at 60 Pa, and changing theplasma power ranging from 20 W to 400 W and the process time rangingfrom 1 second to 10 minutes.

[0180] The results were shown in FIG. 17. The angle was about 60° whenthe core material was not processed yet. After the core material wassubjected to the oxygen-plasma process, the angle changed to about 400to 25°. Whichever recessed mold 10 that had been subjected to theoxygen-plasma process illustrated in FIG. 17 was used, an opticalwaveguide could be manufactured in the same way as Example 10.

EXAMPLE 12

[0181] [Manufacturing of Optical Waveguide 3]

[0182] How an optical waveguide was manufactured will be explained, withreference to FIG. 14. First, a recessed mold 10 was prepared in the sameway as in Example 10, as is illustrated at (a) in FIG. 14. Then, asdepicted at (b) in FIG. 14, oxygen-plasma process was performed on therecessed mold 10.

[0183] In the meantime, a substrate 20 (made of glass) was prepared asshown at (c) in FIG. 14. Ultraviolet-curable epoxy resin was applied, asclad material 2′, to the entire surface of the substrate 20 by mean ofspin coating, and UV-cured.

[0184] Then, as shown at (d) and (e) in FIG. 14, core material 1′ isapplied between the recessed mold 10 and the substrate 20 having a clad2. Ultraviolet rays were applied through the substrate 20, thus forminga core pattern 1.

[0185] After peeling the recessed mold 10, Al was deposited on theinclined surfaces by means of masked vapor deposition, forming metalmirrors 4 and 6 as illustrated at (f) in FIG. 14. As shown at (g) inFIG. 14, ultraviolet-curable epoxy resin was applied, as clad material3′, on the entire surface. Ultraviolet rays were applied, curing theclad material. Thus, an optical waveguide 7 was manufactured.

EXAMPLE 13

[0186] [Manufacturing of Optical Waveguide 4]

[0187] This example will be explained with reference to FIG. 15. First,a projecting mold 16 (made of silicone) was prepared as shown at (a) inFIG. 15, by a method similar to the method of preparing Example 10.Then, as depicted at (b) in FIG. 15, an oxygen-plasma process wasperformed on the projecting mold 16.

[0188] Meanwhile, a substrate 20 (made of glass) was prepared as shownat (c) in FIG. 15. Ultraviolet-curable epoxy resin was applied, as cladmaterial 2′, to the entire surface by means of spin coating. As shown at(d) in FIG. 15, the substrate 20 was laid on the projecting mold 16,with the clad material 2′ contacting the mold 16. Ultraviolet rays wereapplied, transforming the material 2′ to a clad 2.

[0189] Then, as depicted at (e) in FIG. 15, the projection mold 16 ispeeled off. Al was deposited on the inclined surfaces by means of maskedvapor deposition, forming metal mirrors 4 and 6 as illustrated at (f) inFIG. 15.

[0190] Further, as shown at (g) to (h) in FIG. 15, ultraviolet-curableepoxy resin was applied, as clad material 1′, on the entire surface. Allepoxy resin, but that part filled in the recess, was scraped with aspatula 46. Ultraviolet rays are applied to the entire surface, curingthe core material 1′. A core pattern 1 is thereby formed.

[0191] Finally, as shown at (i) in FIG. 15, ultraviolet-curable epoxyresin was applied, as clad material 3′, on the entire surface.Ultraviolet rays are applied, curing the core material 3′. An opticalwaveguide 7 was thereby manufactured.

[0192] <Comparative Example>

[0193] [Manufacturing of Optical Waveguide 5]

[0194] A comparative example will be described with reference to FIG.18. First, a substrate 20 (made of silicone) having a patterned recesswas prepared as shown at (a) in FIG. 18, in the same way as in Example10.

[0195] Next, as depicted at (b) and (c) in FIG. 18, ultraviolet-curableepoxy resin was applied, as core material 1′, on the entire surface, notcarrying out a surface treatment as in Example 10. All epoxy resin, butthat part filled in the recess, was scraped with a spatula 46.Ultraviolet rays are applied to the entire surface, curing the corematerial 1′. A core pattern 1 is thereby formed.

[0196] Core patterns 1 having a width of 100 μm or more and beingcontinuous could easily be made. However, core patterns 1 having a widthof 50 μm or less were hard to be continuous. Core patterns having such asmall width, if formed, were discontinuous.

[0197] As described above, a reliable core pattern can easily be made inthe second embodiment and in Examples 10 to 13. This is because thesubstrate undergoes a surface treatment to enhance its affinity for thecore material, before the core material is filled in the patternedrecess of the substrate. Since the core pattern has inclined surfaces onwhich optical-path changing mirrors will be provided, no process must beperformed to make such inclined surfaces after molding. Metal cantherefore be vapor-deposited on the inclined surfaces right after thecore pattern has been made. In addition, the use efficiency of corematerial is as high as in the first embodiment.

[0198] Thus, polymer optical waveguides that are reliable can bemanufactured at low cost.

[0199] (Third Embodiment)

[0200] A third embodiment of this invention will be described. In thethird embodiment, the light from the light source is converted toparallel beams, which go into a core 1 and improve the connectionefficiency. If the plane mirrors 4 and 6 as depicted in FIG. 47 wereused, the light from the light-emitting element 40 goes into the core 1,preserving its angular distribution. The signal light 8 propagates,preserving the angular distribution, and diverges at a large angle whenit emerges.

[0201] When the mirrors 4 and 6 are concave mirrors, having the focalpoint set almost at the light-emitting point of the light-emittingelement 40, the light beams reflected by the concave mirrors go parallelinto the core, as illustrated in FIG. 19. The light emerging from thecore diverges but at a small angle. This increases the connectionefficiency of light, from the core to the light-receiving element.

[0202]FIG. 19 is a sectional view, showing the focusing of light in onlythe plane of the drawing. If the concave mirror is curved in the planeperpendicular to the drawing, the light is focused in this plane, too.Either characterizes the present invention. When the concave mirrorshave a radius of curvature of 300 μm, the focal distance is about 100μm. The phrase “the focal point set almost at the light-emitting point”means that the component positions in the ±30% region of focal distance.

[0203] The term “focal distance” usually means the distance thatparallel beams applied perpendicular to a mirror and reflected therefromtravel until they meet at a point. For this embodiment of the invention,however, the term means the distance that parallel beams applied at 45to a mirror and reflected therefrom travel until they meet at a point.The focal distance of this definition can not only be measured, but alsobe calculated from the shape of the mirror.

[0204] In the present embodiment, displacement tolerance of thelight-receiving element 41 can be increased, by focusing the light fromthe core 1 to the light-receiving element 41. More precisely, concavemirrors 4 and 6 are so formed that their focal distance 9 is longer thanhalf the distance between the light-receiving element 41 and the mirror.The light 8 can then be almost focused at the surface of thelight-emitting element 41. Thus, the displacement tolerance increases.The displacement tolerance is maximal if the focal distance 9 is nearlyequal to the distance between the concave mirrors and thelight-receiving element 41.

[0205]FIG. 20 is a sectional view, showing the focusing of light in onlythe plane of the drawing. If the concave mirror is curved in the planeperpendicular to the drawing, the light is focused in this plane, too.Either characterizes the present invention. Even if the light is focusedin only the plane of the drawing or the plane perpendicular thereto, anadvantage can be accomplished, which also characterizes this invention.

[0206] If the focal distance 9 is shorter than half the distance betweeneach concave mirror and the light-receiving element 41, the light willdiverge, reducing the displacement tolerance and thus decreasing theconnection efficiency.

[0207] In most cases, the term “focal distance” means the distance fromthe center point of a curved mirror to the point, where light beamsmeets reflected by the mirror meets when parallel light beams areapplied to the mirror. For the present embodiment, however, the term isused to mean the distance from the center point of a curved mirror tothe point where light beams reflected by the mirror meet when parallellight beams are applied at 45° to the direction perpendicular to themirror. The focal distance of this definition can not only be measured,but also be calculated on the basis of the shape of the mirror. Theelements 40 and 41 can easily be adjusted in position, by changing thesize of electrodes or spacers 42 and 43.

[0208] A method of manufacturing the optical waveguide having concavemirrors will be described briefly. At first, a pattern 32 is formed on asubstrate 31 as shown at (a) in FIG. 21. The pattern 32 is made ofphotosensitive resin and has mirror-equivalent surfaces (convexsurfaces) 4′ at ends.

[0209] Next, using the pattern 32, a recessed mold 10 is formed as shownat (b) in FIG. 21. At least the surface region of the mold 10 is made ofsilicon resin. Using the recessed mold 10, an optical waveguide ismanufactured as described below.

[0210] More specifically, core material 1′ in the form of liquid isinterposed between the recessed mold 10 and a substrate 20 having a clad2, as illustrated at (c) in FIG. 21. The core material 1′ is cured asdepicted at (d) in FIG. 21. Then, as shown at (e) in FIG. 21, therecessed mold 10 is peeled off, providing a core pattern 1 that hasmirror surfaces 4.

[0211] Next, as shown at (f) in FIG. 21, reflecting films 6 are formedon the mirror surfaces. Further, as depicted at (g) in FIG. 21, a clad 3is formed, covering the entire surface of the resultant structure.

[0212] This method can produce a core pattern that has inclined convexsurfaces at the ends. These inclined convex surfaces will be concavemirrors. Namely, the convex surfaces serve as convex mirrors for thelight travelling in the core pattern. The reflecting films may be metalfilms or multi-layer dielectric films. Nonetheless, metal films arepreferred because their fluctuation of thickness doesn't influence thereflection.

[0213] The pattern for forming the inclined convex surfaces can be madeby the following three methods.

[0214] In the first method, photolithography, for example, is performed,forming a resist pattern made of photosensitive resin. Thereafter, asshown at (a) to (c) in FIG. 22, laser beams 33 are applied to either endof a photosensitive resin layer 32 formed on the substrate 31. A maskblocks some of the laser beams 33, casting a substantially circularshadow on the end of the resin layer 32. An end part of the resin layer32 is thereby evaporated, forming a mirror-equivalent surface 4′. Thesurface 4′ can collect light beams about the direction perpendicular toboth traveling optical axes. The region outside the “substantiallycircular shadow” is an area that is irradiated with laser beams. Theadjective phrase “substantially circular” means any curved linesincluding a quadric curve.

[0215] In the second method, photolithography is carried out, forming aresist pattern, as shown at (a) in FIG. 23. Then, as depicted at (b) to(f) in FIG. 23, a laser process is repeated several times, applyinglaser beams to either end of a resist, in a different direction eachtime. An inclined convex surface is therefore formed. Instead, the laserprocess may be repeated only a few times, each time applying laser beams33 which have a substantially circular shadow, as is illustrated at (a)to (d) in FIG. 24.

[0216] In the third method, photolithography is carried out, forming aresist pattern as shown at (a) in FIG. 25. Thereafter, a laser processis performed, forming an inclined surface, as illustrated at (b) and (c)in FIG. 25. Then, the temperature is raised, causing the resist to flow,forming a convex surface. The resist can be of either a positive type ora negative type.

EXAMPLE 14

[0217] [Laser Process Casting a Substantially Circular Shadow]

[0218] Example 14 of the third embodiment will be described, withreference to FIG. 22. As depicted at (a) in FIG. 22, a dry film resistwas laid on a substrate 31 (made of glass). The film resist was thenexposed to light through photomask and further developed. Aphotosensitive resin layer 32 was thereby shaped into a core pattern andits height and width were 40 μm.

[0219] Next, laser beams 33 were obliquely applied, from a KrF excimerlaser. A mask blocks some of these beams, casting a substantiallycircular shadow on either end of the resin layer 32, as is illustratedat (b) in FIG. 22. A surface 4′ equivalent to a convex mirror is therebyformed at either end of the resin layer 32. A projecting mold 30 isthereby provided. The circular shadow defined by the laser beams blockedby the mask had a radius of curvature of 300 μm. The resist processedhad a radius of curvature of about 300 μm.

EXAMPLE 15

[0220] [Irradiation Repeated Several Times]

[0221] Example 15 according to the third embodiment will be describedwith reference to FIG. 24. As shown at (a) in FIG. 24, a dry film resistwas laminated to the substrate 31 (made of glass). Using the resist, aphotosensitive resin layer 32 was exposed to light and developed. A corepattern was thereby formed, height and width of which were 40 μm.

[0222] Next, laser beams 33 were obliquely applied, from a KrF excimerlaser. A mask was used, blocking some of these beams, casting asubstantially circular shadow on either end of the resin layer 32, as isillustrated at (b) in FIG. 24. Thus, a laser process was carried out forthe first time.

[0223] Then, as shown at (c) in FIG. 24, the laser process was performedfor the second time. At this time, laser beams were obliquely applied,at an angle that was 100 more or less than in the laser processperformed first. As a result, a surface 4′ equivalent to an inclinedconvex mirror was formed as is illustrated at (d) in FIG. 24. Thecircular shadow defined by the laser beams 33 blocked by the mask had aradius of curvature of 300 μm. The resist processed had a radius ofcurvature of about 300 μm, too.

EXAMPLE 16

[0224] [Reflow]

[0225] Example 16 according to the third embodiment will be describedwith reference to FIG. 25. As shown at (a) in FIG. 25, a resist inliquid state was applied to a substrate 31 (made of glass). Using theresist, a photosensitive resin layer 32 was exposed to light anddeveloped. A core pattern was thereby formed, height and width of whichwere 40 μm.

[0226] Next, laser beams 33 were obliquely applied, from a KrF excimerlaser. A mask was used, blocking some of these beams, casting arectangular shadow on either end of the resin layer 32, as isillustrated at (b) in FIG. 25. Thus, an inclined flat surface was formedat either end of the layer 32. Then, a heat treatment was performed at130° C. for 10 minutes. As a result, the resin flowed at the end of thelayer 32, forming surface 4, equivalent to an inclined convex mirror, asshown at (c) in FIG. 25. The resist processed had a radius of curvatureof about 300 μm.

EXAMPLE 17

[0227] [Manufacturing of the Optical Waveguide]

[0228] Silicone resin in liquid state was applied to the projecting mold30 depicted at (a) in FIG. 21 made by the method of Example 15. Theresin was cured at room temperature. Then, the projecting mold 30 waspeeled off. A recessed mold 10 was thereby made as is illustrated at (b)in FIG. 21.

[0229] Next, a substrate 20 (made of glass) was prepared, andultraviolet-curable epoxy resin was applied, as clad material 2′, to theentire surface by means of spin coating. Ultraviolet rays are applied tothe entire surface at intensity of 4 J/cm². The clad material 2′ wasthereby cured, forming a film (not shown) having a thickness of 30 μm.

[0230] Then, as shown at (c) in FIG. 21, ultraviolet-curable epoxy resinwas dripped, as core material 1′ onto the recessed mold 10. Thesubstrate 20 having a clad 2 was laid on the recessed mold 10 andpressed. As shown at (d) in FIG. 21, the core material 1′ was therebyembedded into the recess of the recessed mold 10. In this condition,ultraviolet rays 12 were applied through the substrate 20 at intensityof 8 J/cm². The core material 1′ was thereby cured, forming a corepattern 1. Then, the recessed mold 10 was peeled off as shown at (e) inFIG. 21. As depicted at (f) in FIG. 21, Al was deposited on the inclinedsurfaces 4 by means of masked vapor deposition. Further, as shown at (g)in FIG. 21, ultraviolet-curable epoxy resin was applied as second cladmaterial 3′. Ultraviolet rays were applied at intensity of 4 J/cm² tothe entire surface. An optical waveguide 7 was thereby formed.

Example 18

[0231] [Evaluation of the Input-Side Mirror]

[0232] An optical waveguide having a concave mirror at one end and aplane mirror at the other end was manufactured by the method of Example17. A vertical-cavity surface-emitting laser (VCSEL) that emits a beamhaving a wavelength of 850 nm was positioned at a distance of 100 μmfrom the center of the waveguide at which the concave mirror wasprovided (i.e., 50 μm from the surface of the waveguide).

[0233] On the other hand, a PD having a diameter of 80 μm was located ata distance of 100 μm from the center of the waveguide at which the planemirror was provided (i.e., 50 μm from the surface of the waveguide).

[0234] The space between the VCSEL and the optical waveguide and thespace between the optical waveguide and the PD were filled withtransparent resin that has almost the same refractive index as the clad.

[0235] The optical signal output from the VCSEL was reflected by theconcave mirror, traveled in the core and reflected by the plane mirror.The optical signal was then applied to the PD. The signal light the PDreceived had intensity 1.5 times greater than the signal light thatemerged from a waveguide that had plane mirrors at both ends.

EXAMPLE 19

[0236] [Evaluation of the Output-Side Mirror]

[0237] An optical waveguide having concave mirrors at both ends wasmanufactured by the method of Example 17. A VCSEL that emits a beamhaving a wavelength of 850 nm and a PD having a diameter of 80 μm waspositioned at a distance of 100 μm from the center of the waveguide(i.e., 50 μm from the surface of the waveguide), respectively.

[0238] The space between the VCSEL and the optical waveguide was filledwith transparent resin that has almost the same refractive index as theclad. The space between the optical waveguide and the PD was filled witha liquid that has almost the same refractive index as the clad.

[0239] The optical signal output from the VCSEL was reflected by theconcave mirror at one end, traveled in the core and reflected by theother end. The optical signal was then applied to the PD.

[0240] The tolerance of the displacement transverse to the PD (i.e., thedisplacement at which the signal intensity falls to 90%) was 30 μm. Onthe other hand, the displacement tolerance for the waveguide having aplane mirror at the output end was 10 μm.

[0241] Examples 14 to 19 of the third embodiment, described above, areadvantageous in the following respects.

[0242] First, the simple structure having concave mirrors used asoptical-path changing mirrors can enhance the connection efficiency andcan increase the displacement tolerance.

[0243] Secondly, the core having concave mirrors can easily be made byusing a mold.

[0244] Thirdly, the laser process casting a substantially circularshadow, the laser process performed repeatedly, or the reflow techniquecan manufacture a mold of core pattern having concave mirrors.

[0245] (Fourth Embodiment)

[0246] A fourth embodiment of this invention will be described. Thefourth embodiment is designed so that optical waveguides may easily bemounted.

[0247] A first characterizing feature of the fourth embodiment is that,as shown in FIG. 26, at least two straight waveguides 45 included in thefirst core A extend in almost the same direction as at least onestraight waveguide 45 included in the other core B.

[0248] That some waveguides extend in almost the same direction as theother waveguides means the difference in direction falls within 10°. Anin-plane mirror 5 is provided at the intersection of the two straightwaveguides included in the first core. The in-plane mirror 5 connectsthe straight waveguides to each other. Preferably, an inclined mirror 4is provided at the end of the waveguide, to connect the waveguide to anexternal element.

[0249] This structure has the following merits.

[0250] The first merit is a decrease in the minimum area that isrequired to change the path direction. This is accomplished by the useof the in-plane mirror 5.

[0251] The second merit is caused by a decrease in the number ofdirections in which the straight waveguide 45 may extend. If the numberof directions is reduced to two, for example, the number of direction ofthe in-plane mirror can be decreases to four, and the number of anglesat which the optical path is changed can be reduced to two.

[0252] For example, the straight waveguide 45 may extend in theX-direction and the Y-direction as is illustrated in FIG. 27A. Then, thein-plane mirror 5 can change the direction of the optical path in fourdifferent manners. That is, it changes the direction from +X-directionto +Y-direction, or vice versa; from +X-direction to −Y-direction, orvice versa; from −X-direction to +Y-direction, or vice versa; or from−X-direction to −Y-direction, or vice versa. The angle by which the+X-direction is changed to +Y-direction, or vice versa, is equal to theangle by which the −X-direction is changed to the −Y-direction, or viceversa. And the angle by which the +X-direction is changed to the−Y-direction, or vise versa, is equal to the angle by which the−X-direction is changed to the +Y-direction, or vice versa. Thus, thereare two angles by which one direction is changed to another. As FIG. 27Bshows, each inclined mirror can extend in four directions, i.e.,+X-direction, −X-direction, +Y-direction and −Y-direction.

[0253] As displayed in FIGS. 27A and 27B, the X-direction and theY-direction need not intersect at right angles. Nonetheless, if theyintersect at right angles as shown in FIG. 28A, the in-plane mirror willchange the direction of the optical path by an angle (i.e., 90°). AsFIG. 28B shows, four types of inclined mirrors 4 are available.

[0254] This configuration renders it easy to provide a surface 5′ and asurface 4′ that are equivalent to an inclined mirror and an inclinedmirror, respectively.

[0255] To form mirror-equivalent surfaces at a time by means of a laserprocess, the process needs to be repeated four times to form surfaces 5′equivalent to the in-plane mirrors, and four times to form surfaces 4′equivalent to the inclined mirrors. Namely, it suffices to repeat thelaser process only eight times in all. If the surfaces 5′ equivalent tothe in-plane mirrors are formed by another method, the laser processneeds to be carried out four times only.

[0256] A laser may be used to process a sample point by point. In thiscase, too, it suffices to set the sample only eight times. To form thesurfaces equivalent to in-plane mirrors, it suffices to set the sampleonly four times.

[0257] The sample needs to be set but less times, depending on thepattern of the sample. The structure of FIG. 26, for example, has fourin-plane mirrors and three inclined mirrors. To produce a mold for thisstructure, the laser process must be repeated seven times, or the samplemust set seven times. If the surfaces 5′ equivalent to the in-planemirrors are formed by another method, it suffices to perform the laserprocess or the sample setting only three times.

[0258] By contrast, the waveguide needs large area and the laser processmust be repeated many times, or the sample must be set many times, inorder to manufacture the conventional waveguide shown in FIG. 48. Thisis because this waveguide has inclined mirrors that are orientated invarious directions.

[0259] A second characterizing feature of the fourth embodiment is thecore width of the in-plane mirrors 5. As FIG. 29 shows, a core 1 isformed on the first clad 2. Reflecting films 6 are formed on those partsof the core 1 which will be inclined mirrors 4 and in-plane mirrors 5. Asecond clad 3 is then formed, covering the first clad 2 and the core 1.In this structure, the shapes of the mirrors are important in themanufacture of this waveguide.

[0260] As shown in FIG. 30, the projection of the in-plane mirror 5, ona plane extending at right angles to the input-side straight waveguide45 i, has a width b that is greater than the width a of the core of theinput-side straight waveguide 45 i. This reduces a loss at the in-planemirror 5.

[0261] Moreover, the output-side straight waveguide 45 o may have a corewidth d greater than the projection width c of the in-plane mirror 5 ona plane perpendicular to the output-side straight waveguide 45 o, as isillustrated in FIG. 31.

[0262] Why it should be so will be explained. In any waveguide, lightguided at a little cladside from the boundary, so most of light travelsin the core, but a little in cladside. If the width b is equal to theprojection width a of the input-side straight waveguide 45 i, the partof the light in the clad would not be reflected. It would inevitably belost or become a crosstalk.

[0263] In the present embodiment, a loss of light is small. This isbecause the light in the clad temporarily enters the core since theprojection width b of the in-plane mirror 5 on the plane perpendicularto the input-side straight waveguide 45 i, is greater than the corewidth a of the input-side straight waveguide 45 i.

[0264] There is another function. An example will be described, in whichthe core pattern is produced by means of photolithography. If aprojecting mold 30 is be made by using a photomask 35 in which b″=a″ asshown at (a) in FIG. 32, b′ will be less than a′ in the projecting mold30 as is illustrated at (b) FIG. 32. This phenomenon is likely to occurdue to diffraction and defocus or fast development at any bendingportion.

[0265] Width b″ of the photomask 35 pertains to the mask pattern 5″ ofthe in-plane mirror, projected on the input-side straight waveguide.Width a″ of the photomask 35 pertains to the mask pattern 45 i of theinput-side waveguide 45 i. Width b′ of the photo-sensitive resin layer32 of the projecting mold 30 pertains to the surface 5′ projected, whichis equivalent to the in-plane mirror located at the bending portion.Width a′ of the photosensitive resin layer 32 of the projecting mold 30is the width a′ of the straight waveguide.

[0266] There is the tendency of: b′<a′. Hence, the width b of thein-plane mirror 5 of the core 1, projected, is less than the width a ofthe straight waveguide.

[0267] This phenomenon can be cancelled out if the core pattern of thephotomask 35 is so shaped that width b″ is greater than width a″ (b″>a″)as depicted in FIG. 30 and FIG. 31.

[0268] In the photolithography performed to from a core pattern, it isdesirable to use a plurality of straight waveguide patterns and aphotomask having the pattern of the in-plane mirror like this.

[0269] A third characterizing feature of the fourth embodiment is thecore width of the inclined mirrors 4. As FIG. 29 shows, a core 1 isformed on the first clad 2. Reflecting films 6 are formed on those partsof the core 1 which will be inclined mirrors 4 and in-plane mirrors 5. Asecond clad 3 is then formed, covering the first clad 2 and the core 1.A waveguide is thereby manufactured. The shapes of the mirrors areimportant to the method of manufacturing of this waveguide. In thismethod, the core width f of each inclined mirror 4 may be greater thanthe core width e of the straight waveguide 45 as is illustrated in FIG.33. Then, the loss of light at the inclined mirror 4 can be reduced. Itmay suffice to make the core width of only the output-side mirror 4 ogreater than the core width e, as depicted in FIG. 34.

[0270] Why it should be so will be explained. In any waveguide, lightguided at a little cladside from the boundary, so most of light travelsin the core of the waveguide, but a little in cladside. If the corewidth f of the inclined mirror 4 is equal to the core width e of thestraight waveguide 45, the part of the light in the clad will not bereflected. It would inevitably be lost or become a crosstalk. In thepresent embodiment, a loss of light is small. This is because the lightin the clad temporarily enters the core since the core width f of theinclined mirror 4 is greater than the core width e of the straightwaveguide 45 as shown at (d) in FIG. 33.

[0271] Another function is performed. The core pattern may be made bymeans of photolithography, and the inclined-mirror pattern 4″ of thephotomask 35 may have width f″ equal to the width e″ of the straightwaveguide pattern 45. Nevertheless, the mirror-equivalent surface 4′ ofthe photosensitive resin layer 32 of the projection mold 30 will have aprojected width f′ that is less than the width e′ of the straightwaveguide as is illustrated at (b) to (c) in FIG. 35. The projectedwidth f of the inclined mirror 4 formed on the core 1 becomes less thanthe width e of the straight waveguide as is shown at (d) in FIG. 35.This phenomenon is likely to occur due to diffraction and defocus orfast development at any end portion. Nonetheless, this phenomenon can becancelled out if the core width f″ of the photomask 35, for the inclinedmirror 4″, is made greater than the core width e″ of the straightwaveguide 45″ as is illustrated in FIG. 33 and FIG. 34.

EXAMPLE 20

[0272] [Process]

[0273] Example 20 according to the fourth embodiment will be describedwith reference to FIG. 29. FIG. 29 shows one core of the opticalwaveguide as shown in FIG. 26.

[0274] First, a dry film resist having a thickness of 40 μm waslaminated to the substrate 31 (made of glass). Using a photomask havingpatterns of straight waveguides that intersect with one another at rightangles and patterns of the in-plane mirrors included in thesewaveguides, the structure was exposed to light and developed.

[0275] A projecting pattern, or a photosensitive resin pattern 32, wasthereby formed. As shown at (a) in FIG. 29, this pattern hadstraight-waveguide equivalents 45′ and surfaces 5′ equivalent toin-plane mirrors.

[0276] Next, laser beams were obliquely applied, thereby formingsurfaces 4′ equivalent to inclined mirrors as is depicted at (b) in FIG.29. Thus, a projecting mold 30 was produced.

[0277] Then, silicone resin in liquid state was applied to theprojecting mold 30 and cured, thus forming a silicone layer. The siliconlayer was peeled off. As a result, a recessed mold 10 was produced asshown at (c) in FIG. 29.

[0278] As shown at (d) in FIG. 29, a substrate 20 (made of glass) wasprepared. An epoxy resin layer having a thickness of 30 μm was formed,as a clad 2, on the substrate 20. Thereafter, using the recessed mold 10made of silicone, a core 1 made of epoxy resin was formed.

[0279] Then, as shown at (e) in FIG. 29, aluminum (Al) wasmask-deposited, forming reflecting films 6 and thus providing mirrors 4and 5. As depicted at (f) in FIG. 29, an epoxy resin layer was formed asclad 3. A waveguide was thereby formed, which were peeled from thesubstrate.

EXAMPLE 21

[0280] [Waveguide 1]

[0281] The same process as employed in Example 20 was performed,manufacturing a waveguide shown in FIG. 26. In producing the mold,surfaces 5′ equivalent to in-plane mirrors were formed byphotolithography, and surfaces 4′ equivalent to inclined mirrors wereformed by obliquely applying laser beams. Since the inclined mirrorswere oriented in only three directions, it sufficed to set the samplethree times only. A single-mode fiber was placed near the inclinedmirror 4 provided at one end of the waveguide. Infrared light having awavelength of 0.85 μm was applied from the fiber to this inclined mirror4. It was confirmed that infrared light emerged from the inclined mirror4 provided at the other end of the waveguide.

EXAMPLE 22

[0282] [In-Plane Mirror 1]

[0283] The process of Example 20 was performed, in which a photomask 35shown at (a) in FIG. 30 was used, thereby forming an in-plane mirror 5as is illustrated at (b) to (c) in FIG. 30. Width a was 40 μm, and widthb was 50 μm. A single-mode fiber was placed near one end of thewaveguide. Infrared light having a wavelength of 0.85 μm was appliedfrom the fiber to this end of the waveguide. The light emerging from theother end of the waveguide was applied to a hard polymer cladding fiber.The loss made in a waveguide having the same length was subtracted fromthe loss made in the waveguide having the in-plane mirror 5. As aresult, the loss at the in-plane mirror 5 was estimated to be about 1dB.

EXAMPLE 23

[0284] [In-Plane Mirror 2]

[0285] The process of Example 20 was performed, in which a photomask 35shown at (a) in FIG. 31 was used, thereby forming an in-plane mirror 5as is illustrated at (b) to (c) in FIG. 31. Width a was 40 μm, width bwas 50 μm, width c was 50 μm, and width d was 50 μm. A single-mode fiberwas placed near one end of the waveguide. Infrared light having awavelength of 0.85 μm was applied from the fiber to this end of thewaveguide. The light emerging from the other end of the waveguide wasapplied to a hard polymer cladding fiber. The loss made in a waveguidehaving the same length was subtracted from the loss made in thewaveguide having the in-plane mirror 5. As a result, the loss at thein-plane mirror 5 was estimated to be about 1 dB.

[0286] <Comparative Example>

[0287] [In-Plane Mirror 3]

[0288] The process of Example 20 was performed, in which a photomask 35shown at (a) in FIG. 32 was used, thereby forming an in-plane mirror 5as is illustrated at (b) to (c) in FIG. 32. Width a was 40 μm, and widthb was 35 μm. A single-mode fiber was placed near one end of thewaveguide. Infrared light having a wavelength of 0.85 μm was appliedfrom the fiber to this end of the waveguide. The light emerging from theother end of the waveguide was applied to a hard polymer cladding fiber.The loss made in a waveguide having the same length was subtracted fromthe loss made in the waveguide having the in-plane mirror 5. As aresult, the loss at the in-plane mirror 5 was estimated to be about 2dB.

EXAMPLE 24

[0289] [Inclined Mirror 1]

[0290] The process of Example 20 was performed, in which a photomask 35shown at (a) in FIG. 33 was used, thereby forming an inclined mirror 4as is illustrated at (b) to (d) in FIG. 33. Width a was 40 μm, and widthb was 50 μm. A single-mode fiber was placed near one end of thewaveguide. Infrared light having a wavelength of 0.85 μm was appliedfrom the fiber to this end of the waveguide. The light emerging from theinclined mirror provided on the other end of the waveguide was appliedto a hard polymer cladding fiber. The loss made in a waveguide havingthe same length was subtracted from the loss made in the waveguide, asmeasured at the inclined mirror 4 used as output side. As a result, theloss at the inclined mirror 4 was estimated to be about 1 dB.

[0291] <Comparative Example 3>

[0292] [Inclined Mirror 2]

[0293] The process of Example 20 was performed, in which a photomask 35shown at (a) in FIG. 35 was used, thereby forming an inclined mirror 4as is illustrated at (b) to (d) in FIG. 35. Width a was 40 μm, and widthb was 35 μm. A single-mode fiber was placed near one end of thewaveguide. Infrared light having a wavelength of 0.85 μm was appliedfrom the fiber to this end of the waveguide. The light emerging from theinclined mirror provided on the other end of the waveguide was appliedto a hard polymer cladding fiber. The loss made in a waveguide havingthe same length was subtracted from the loss made in the waveguide, asmeasured at the inclined mirror 4 used as output side. As a result, theloss at the in-plane mirror 4 was estimated to be about 2 dB.

EXAMPLE 25

[0294] [Inclined Mirror 3]

[0295] The process of Example 20 was performed, in which a photomask 35shown at (a) in FIG. 34 was used, thereby forming an inclined mirror 4as is illustrated at (b) to (d) in FIG. 34. Width a was 40 μm, and widthb was 50 μm. A single-mode fiber was placed near the inclined mirror 4i. Infrared light having a wavelength of 0.85 μm was applied from thefiber to the waveguide. The light emerging from the inclined mirror 4 oprovided on the other end of the waveguide was applied to a hard polymercladding fiber. The loss made when the light was applied in a reversedirection was about 1 dB greater than the loss made when the light wasapplied in the designed direction.

[0296] The fourth embodiment and Examples 20 to 25, all described above,can achieve the following advantages.

[0297] First, the in-plane mirror can decrease the area that is requiredto change the direction. Second, since the straight waveguides areorientated in a limited number of directions, the number of orientationsof the in-plane mirrors and inclined mirrors can be decreased. Thisrenders it easy to manufacture the waveguides. Third, the in-planemirrors and inclined mirrors can have a large width, which helps toreduce the loss.

[0298] Hence, it is possible to provide optical waveguides in which acore can be easily formed to connect many given points.

[0299] (Fifth Embodiment)

[0300] A fifth embodiment of the present invention will be described. Inthe fifth embodiment, spacers and/or alignment bases are used to providea gap and/or a position between an optical waveguide and anothersubstrate when the waveguide, which is of the same type as the first tofourth embodiments, is bonded to another substrate.

[0301] As shown at (a) in FIG. 36, an optical waveguide 7 has spacers 71that are taller than the core 1. The optical waveguide 7 is bonded toanother substrate 60 by using clad material 3′ as is illustrated at (b)in FIG. 36. After the waveguide 7 is so bonded, the difference (hs-hc)between the height hs of the spacers 71 and the height hc of the core 1determines a thickness for the second clad 3. The distance from theseparate substrate 60 to the core 1 can therefore precisely becontrolled. When the substrate 20 is peeled from the optical waveguide7, a laminated structure is obtained as is depicted at (c) in FIG. 36.

[0302] The spacers 71 may be made of a material different from the core1. It is desired, nonetheless, that the spacers 71 be made of the samematerial as the core 1. If they are made of the same material as thecore 1, such a process as depicted in FIG. 38 can be carried out. Asshown at (a) in FIG. 38, a resist pattern 32 for the core is formed on asubstrate 31 by means of photolithography. As shown at (b) in FIG. 38,laser beams 33 are obliquely applied, forming inclined surfaces 4′ atthe ends of the resist pattern 32. Next, as shown at (c) in FIG. 38,members 71′ having a predetermined thickness are bonded to the substrate31, not to the core, thus making a projecting mold 30. As depicted at(d) in FIG. 38, silicone is applied to the projecting mold 30, thusforming a silicone mold 10. As shown at (e) in FIG. 38, a core material1′ is applied between the silicon mold 10 and the substrate 20 having afirst clad 2. The core material 1′ is cured as is illustrated at (f) inFIG. 38. The silicone mold 10 is peeled. Spacers 71 are thereby made atthe same time the core pattern 1 is produced. As shown at (h) in FIG.38, metal films 6 are formed on the inclined surfaces 4′ of the corepattern 1. The metal films 6 serve as mirrors.

[0303] The metal films 6 can be formed by various steps, such as (i)mask vapor deposition, (ii) photo-lithography and etching performedafter deposition of metal film, or (iii) photolithography, depositionand lift-off process. The metal films 6 may be made of Al, Au, Pt, Ag,Cu or Ti, or an alloy of these metals. Made of any one of thesematerials, the films 6 can make desirable mirrors.

[0304] Alternatively, such a method as shown in, for example, FIG. 39may be carried out. As depicted at (a) in FIG. 39, a first negative-typeresist is formed on the substrate 31. A core pattern 32 and spacer molds71 a′, all provided on the substrate 31, are exposed to light. A secondnegative-type resist is then formed. Spacer molds 71 b′ provided on thespacer molds 71 a′ are exposed to light. The resultant structure isdeveloped in its entirety. Spacer molds 71′ are thereby formed. Thespacer molds 71′ are taller than the photosensitive resin layer 32having the same shape as the core to be formed.

[0305] As illustrated at (b) in FIG. 39, laser beams 33 are obliquelyapplied, thereby forming, at the ends of the core pattern 32, surfaces4′ which are equivalent to inclined mirrors. As a result, a projectingmold 30 is made. Thereafter, a core 1 and spacers 71 are formed on thefirst clad 2 of the substrate 20 as shown at (c) to (f) in FIG. 39, inthe same way as is illustrated at (d) to (g) in FIG. 38.

[0306] Next, as shown at (g) in FIG. 39, metal films, or reflectingfilms 6, are formed on the surfaces 4 of the core pattern, which areequivalent to the inclined mirrors.

[0307] When the optical waveguide 7 is bonded to another substrate 60 byusing clad material 3′ as shown at (a) to (c) in FIG. 37, the spacers 71are fitted into the recesses 63 made on the separate substrate 60. Thus,the optical waveguide 7 is automatically aligned with the substrate 60,providing a laminated structure.

[0308] The fifth embodiment has alignment marks 70, which facilitate themutual positioning of the optical waveguide 7 and another substrate 60.More precisely, the optical waveguide 7 according to this embodiment hasalignment marks 70. As shown at (a) in FIG. 40 or at (a) in FIG. 41, thealignment marks 70 are provided at the same level as, or at a levelhigher than, the core 1.

[0309] As depicted at (b) in FIG. 40 or at (b) in FIG. 41, the opticalwaveguide 7 can be accurately positioned when it is bonded to anothersubstrate 60. This is because each alignment mark 70 is spaced a littlefrom the corresponding alignment mark 61. Then, the substrate 20 ispeeled from the optical waveguide 7. A laminated structure is therebyobtained, as illustrated at (c) in FIG. 40 or at (c) in FIG. 41.

[0310] The material of alignment marks 70 can be the same as the metalfilms 6 for mirrors, or different. If they are the same, it will beeasier to manufacture the waveguide as seen from FIG. 42. For example,such a step as shown in FIG. 42 may be performed. As shown at (a) inFIG. 42, a resist pattern is formed on the substrate 31 byphotolithography, thus providing a core pattern 32 and alignment markbases 72′. Note that the core pattern 32 and the bases 72′ for thealignment marks are made of the same resist and therefore have the sameheight. Thereafter, as depicted at (b) to (f) in FIG. 42, the corepattern 1 and the bases 72 for the alignment marks are formed on thefirst clad 2 provided on the substrate 20, in the same manner asillustrated at (b) to (f) in FIG. 38.

[0311] Next, as shown at (g) in FIG. 42, metal films are formed on theinclined surfaces 4 of the core pattern 1 and on the alignment bases 72.Mirrors and alignment marks 70 are thereby formed. Then, as shown at (h)in FIG. 42, a second clad 3 is formed, covering the core pattern 1,bases 72 and first clad 2. As a result, an optical waveguide 7 is formedon the substrate 20 as is illustrated at (g) or (h) in FIG. 42.

[0312] Alternatively, the waveguide may be manufactured by, for example,the method shown in FIG. 43. As depicted at (a) in FIG. 43, a firstnegative-type resist is formed on the substrate 31. Then, the corepattern 32 and the bases 72 a′ for alignment marks are exposed to light.A second negative-type resist is formed, and the bases 72 b′ on thebases 72 a′ are exposed to light. Then, the entire structure isdeveloped. Bases 72′ are thereby formed, which are taller than the corepattern 32 by the height of he second negative-type resist.

[0313] As shown at (b) in FIG. 43, laser beams 33 are obliquely applied,forming, at the ends of the core pattern 32, surfaces 4′ which areequivalent to inclined mirrors. As a result, a projecting mold 30 ismade. Thereafter, a core 1 and bases 72 for alignment marks are formedon the first clad 2 of the substrate 20 as shown at (c) to (f) in FIG.43, in the same way as is illustrated at (c) to (f) in FIG. 38.

[0314] Next, as shown at (g) in FIG. 43, metal films, or reflectingfilms 6 are formed on the surfaces 4 of the core pattern, and at thesame time, alignment marks 70 are formed on the bases 72. In this case,the bases 72 for the alignment marks can serve as spacers.

[0315] The metal films 6 and 70 can be formed by carrying out steps (i)to (iii) that have been described earlier. The material of these filmsmay be one of the metals specified above or an alloy thereof. Then,desirable mirrors and desirable alignment marks 70 can be formed. Thepositions of the alignment marks 70 are determined on the basis of theposition of the core pattern 1 and the positions of the mirrors 4. Thealignment marks 70 made of metal may be determined on the basis of otheralignment marks (not shown) made of core material.

[0316] Hitherto described are optical waveguides each having mirrors atits ends. Each waveguide may be replaced by an optical waveguide thathas no mirrors or an optical waveguide that has in-plane mirrors.

EXAMPLE 26

[0317] [Optical Waveguide Having Spacers]

[0318] Example 26 of the fifth embodiment will be described, withreference to FIG. 38. As shown at (a) in FIG. 38, a dry film resist waslaminated to the substrate 31 (made of glass). The resist was exposed tolight through photomask and developed, thus forming a resist pattern 32.The resist pattern 32 was shaped like a waveguide to be formed and itsheight and width were 40 μm.

[0319] Next, as illustrated at (b) in FIG. 38, laser beams 33 wereobliquely applied from a KrF excimer laser, thus forming inclinedsurfaces 4′ at the ends of the resist pattern 32.

[0320] Then, as shown at (c) in FIG. 38, a tape of 70 μm thick wasbonded to the substrate 31, providing spacers 71′. A projecting mold 30was thereby produced.

[0321] Further, silicone resin in liquid state was applied to theprojecting mold 30 and cured, thus forming a silicone layer. The siliconlayer was peeled off. As a result, a recessed mold 10 was produced asshown at (d) in FIG. 38. Then, a substrate 20 (made of glass) wasprepared. Ultraviolet-curable epoxy resin was applied, as clad material2′, to the entire surface by means of spin-coating. Ultraviolet rays areapplied to the entire surface at intensity 4 J/cm². The clad material 2′was thereby cured, forming a film having a thickness of 30 μm (notshown).

[0322] Then, as shown at (e) to (f) in FIG. 38, ultraviolet-curableepoxy resin was dripped, as core material 1′ onto the recessed mold 10.The substrate 20 having a clad 2 was laid on the recessed mold 10 andpressed. The core material 1′ was thereby embedded into the recess ofthe recessed mold 10. In the condition shown at (f) in FIG. 38,ultraviolet rays 12 were applied through the substrate 20 at intensityof 8 J/cm². The core material 1′ was cured, forming a core pattern 1.

[0323] The recessed mold 10 was peeled off as shown at (g) in FIG. 38.As depicted at (h) in FIG. 38, Al was deposited on the inclined surfaces4 of the by means of masked vapor deposition.

EXAMPLE 27

[0324] [Transfer of the Optical Waveguide Having Spacers]

[0325] Example 27 of the fifth embodiment will be described, withreference to FIG. 36. As depicted at (a) in FIG. 36, ultraviolet-curableepoxy resin was applied on an optical waveguide 7. The waveguide 7 waslaid on another substrate 60. Ultraviolet rays were applied through thesubstrate 20 at intensity 4 J/cm² as is illustrated at (b) in FIG. 36. Asecond clad 3, or adhesive layer 62, was thereby cured. As shown at (c)in FIG. 36, the substrate 20 was peeled off, thus providing a laminatedstructure.

EXAMPLE 27A

[0326] [Optical Waveguide 2 Having Spacers]

[0327] Example 27A of the fifth embodiment will be described, withreference to FIG. 39. As depicted at (a) in FIG. 39, a dry film resistwas laminated to the substrate 31 (made of glass). A core pattern 32 andthe spacer mold 71 b′ were exposed to light. Further, a second dry filmresist was bonded, and the spacer mold 71 a′ was exposed to light.Thereafter, the structure was developed, producing a spacer mold 71′that had a core pattern 32 and a height of 70 μm. The core pattern 32had height and width of 40 μm.

[0328] Next, as depicted at (b) in FIG. 39, laser beams 33 wereobliquely applied from a KrF excimer laser, thus forming inclinedsurfaces 4′ at the ends of the resist pattern 32 made of photosensitiveresin. As a result, a projecting mold 30 was made.

[0329] Silicone resin in liquid state was applied to the projecting mold30 and cured at room temperature. Then, the projecting mold 30 waspeeled off. A recessed mold 10 was thereby made as is illustrated at (c)in FIG. 39.

[0330] Then, a substrate 20 (made of glass) was prepared.Ultraviolet-curable epoxy resin was applied, as clad material 2′ bymeans of spin-coating. Ultraviolet rays are applied to the entiresurface at intensity 4 J/cm². The clad material 2′ was thereby cured,forming a layer (not shown) having a thickness of 30 Ξm.

[0331] As shown at (d) to (e) in FIG. 39, ultraviolet-curable epoxyresin was dripped, as core material 1′ onto the recessed mold 10. Thesubstrate 20 having a clad 2 was laid on the recessed mold 10 andpressed. The core material 1′ was thereby embedded into the recess ofthe recessed mold 10.

[0332] In the condition shown at (e) in FIG. 39, ultraviolet rays wereapplied through the substrate 20 at intensity of 8 J/cm². The corematerial 1′ was cured, forming a core pattern 1 and spacers 71. Next, asdepicted at (f) in FIG. 39, the recessed mold 10 was peeled off, and Alwas vapor-deposited on the entire surface, forming resist patterns onthe surfaces 4 that are equivalent to inclined mirrors. Etching usingmixture of phosphorus acid and nitric acid was carried out, and theresist was removed. As a result, reflecting films 6 were formed as isillustrated at (g) in FIG. 39.

EXAMPLE 27B

[0333] [Transfer 2 of the Optical Waveguide Having Spacers]

[0334] Example 27B of the fifth embodiment will be described, withreference to FIG. 37. As depicted at (a) in FIG. 37, ultraviolet-curableepoxy resin was applied to an optical waveguide 7. The waveguide waslaid on another substrate 60 having recesses 63, with spacers 71 fittedin the recesses 63. The waveguide and the substrate 60 wereautomatically positioned with respect to each other. Ultraviolet raysare applied through the substrate 20 to the entire surface at intensity4 J/cm². The second clad 3, or adhesive 62, was thereby cured. As shownat (c) in FIG. 37, the substrate 20 was peeled off, thus providing alaminated structure.

EXAMPLE 28

[0335] [Optical Waveguide Having Alignment Marks]

[0336] Example 28 of the fifth embodiment will be described, withreference to FIG. 42. As depicted at (a) in FIG. 42, a dry film resistwas laminated to the substrate 31 (made of glass). The resist wasexposed to light and developed, forming a resist pattern 32 and bases72′ for alignment marks. The resist pattern 32 had a cross sectionshaped like a waveguide to be made. The height and width were 40 μm.

[0337] Next, laser beams 33 were obliquely applied from a KrF excimerlaser, thus forming inclined surfaces 4′ at the ends of the resistpattern 32. As a result, a projecting mold 30 was made.

[0338] Silicone resin in liquid state was applied to the projecting mold30 and cured at room temperature. Then, the projecting mold 30 waspeeled off. A recessed mold 10 was thereby made as is illustrated at (c)in FIG. 42.

[0339] Then, a substrate 20 (made of glass) was prepared.Ultraviolet-curable epoxy resin was applied, as clad material 2′ bymeans of spin-coating. Ultraviolet rays are applied to the entiresurface at intensity of 4 J/cm². The clad material 2′ was thereby cured,forming a layer (not shown) having a thickness of 30 μm.

[0340] As shown at (d) to (f) in FIG. 42, a core pattern 1 and bases 72were formed on the first clad 2 provided on the substrate 20, in thesame way as is illustrated at (e) to (g) in FIG. 38.

[0341] Al was vapor-deposited on the entire surface, forming resistpatterns on the bases 72 for alignment marks and on the surfaces 4 thatare equivalent to inclined mirrors. Etching using the mixture ofphosphoric acid and nitric acid was carried out, and the resist wasremoved. As a result, alignment marks 70 and reflecting films 6 wereformed as is illustrated at (g) in FIG. 42. Ultraviolet-curable epoxyresin was applied to the entire surface of the resultant structure.Ultraviolet rays were then applied at intensity 4 J/cm², thusmanufacturing a second clad 3, as is illustrated at (h) in FIG. 42.

EXAMPLE 29

[0342] [Transfer of the Optical Waveguide Having Alignment Marks]

[0343] Example 29 of the fifth embodiment will be described, withreference to FIG. 40. As shown at (a) in FIG. 40, ultraviolet-curableepoxy resin was applied to an optical waveguide 7. The waveguide waslaid on another substrate 60. The waveguide was positioned with respectto the substrate 60, by using alignment marks 70. Ultraviolet rays areapplied through the substrate 20 to the entire surface at intensity 4J/cm². An adhesive layer 62 was thereby cured as shown at (b) in FIG.40. Finally, the substrate 20 was peeled off, thus providing such alaminated structure as depicted at (c) in FIG. 40.

EXAMPLE 30

[0344] [Optical Waveguide Having Spacers and Alignment Marks]

[0345] Example 30 of the fifth embodiment will be described, withreference to FIG. 43. A dry film resist was laminated to the substrate31 (made of glass). A core pattern 32 and bases 72 a′ for alignmentmarks (or spacer molds) were exposed to light. Further, a second dryfilm resist was laminated, and base molds 72 b′ (or spacer mold) wereexposed to light. Thereafter, the structure was developed, producingalignment-mark base mold 72′ (which was also spacer mold) and corepattern 32 as depicted at (a) in FIG. 43. Height of the base mold was 70μm and the height and width of the core pattern 32 were 40 μm.

[0346] Next, as shown at (b) in FIG. 43, laser beams 33 were obliquelyapplied from a KrF excimer laser, thus forming inclined surfaces 4′ onthe resist pattern 32. As a result, a projecting mold 30 was made.

[0347] Silicone resin in liquid state was applied to the projecting mold30 and cured at room temperature. Then, the projecting mold 30 waspeeled off. A recessed mold 10 was thereby made as is illustrated at (c)in FIG. 43.

[0348] Then, a substrate 20 (made of glass) was prepared.Ultraviolet-curable epoxy resin was applied, as clad material 2′ bymeans of spin-coating. Ultraviolet rays are applied to the entiresurface at intensity 4 J/cm². The clad material 2′ was thereby cured,forming a film (not shown) having a thickness of 30 μm.

[0349] As shown at (d) to (e) in FIG. 43, ultraviolet-curable epoxyresin was dripped, as core material 1′ onto the recessed mold 10. Thesubstrate 20 having a clad 2 was laid on the recessed mold 10 andpressed. The core material 1′ was thereby embedded into the recesses ofthe recessed mold 10.

[0350] In the condition shown at (e) in FIG. 43, ultraviolet rays wereapplied through the substrate 20 at intensity of 8 J/cm². The corematerial 1′ was cured, forming a core pattern 1 and bases 72 foralignment marks base 72 (or spacers 71). Next, as depicted at (f) inFIG. 43, the recessed mold 10 was peeled off, and Al was vapor-depositedon the entire surface, forming resist patterns at the positions wherealignment marks are to be formed and on the surfaces 4 that areequivalent to inclined mirrors. Etching using the mixture of phosphoricacid and nitric acid was carried out, and the resist was removed. As aresult, alignment marks 70 and reflecting films 6 were formed as isillustrated at (g) in FIG. 43.

EXAMPLE 31

[0351] [Transfer of the Optical Waveguide Having Spacers and AlignmentMarks]

[0352] Example 31 of the fifth embodiment will be described, withreference to FIG. 41. Ultraviolet-curable epoxy resin was applied to anoptical waveguide 7 as depicted at (a) in FIG. 41. As shown at (b) inFIG. 41, the waveguide was laid on another substrate 60, and ultravioletrays are applied through the substrate 20 to the entire surface atintensity 4 J/cm², thereby curing the second clad 3, or adhesive layer62. Finally, the substrate 20 was peeled off as is illustrated at (c) inFIG. 41. As a result, a laminated structure was obtained.

[0353] The fifth embodiment and Examples 26 to 31 thereof, all describedabove, can achieve the following advantages.

[0354] First, the use of spacers can precisely control the height of theoptical waveguide, and the second clad, which serves as an adhesivelayer, can simplify the manufacture of the waveguide. Second, thealignment marks can precisely control the position of the opticalwaveguide, because they lie at a level as same as or higher than the topof the core.

[0355] Hence, the optical waveguide and another substrate can beaccurately spaced apart and positioned with respect to each other. Thus,the optical waveguide is fit to be bonded to another substrate.

[0356] The present invention can provide a method of manufacturing anoptical waveguide which is inexpensive and in which the core is used athigh efficiency and scarcely deformed. Further, the invention canprovide an optical waveguide that excels in mirror-connectionefficiency, which has a large tolerance for element displacement andwhich is simple in structure and inexpensive. In addition, thisinvention can provide an optical waveguide in which a core can be easilyformed to connect many given points. Moreover, the invention can providean optical waveguide which can be spaced from, and positioned withrespect to, another substrate and is suitable for piling up.

What is claimed is:
 1. A method of manufacturing an optical waveguidehaving a core and a clad, comprising: a step of forming a first clad byapplying a resin on a substrate and curing the resin; a step of applyinga core material between a recessed mold which has a recess having ashape identical to a shape of the core and the first clad which isprovided on the substrate; a step of curing the core material thusburied, thereby forming a core pattern having a shape identical to thatof the recess; and a step of peeling the recessed mold from the corepattern and the first clad.
 2. The method of manufacturing an opticalwaveguide, according to claim 1, wherein the step of curing the corematerial includes a step of applying ultraviolet rays to the corematerial through the substrate and the first clad, thereby curing thecore material.
 3. The method of manufacturing an optical waveguide,according to claim 1, wherein the step of applying a core material isperformed by using press rolls.
 4. The method of manufacturing anoptical waveguide, according to claim 3, wherein an angle between adirection 11 a in which the press rolls move and a main straight part ofthe recess of the recessed mold is about 45° or less.
 5. The method ofmanufacturing an optical waveguide, according to claim 1, furthercomprising a step of applying a resin, covering the core pattern and thefirst clad, and curing the resin, thereby to form a third clad.
 6. Themethod of manufacturing an optical waveguide, according to claim 1,further comprising a step of removing a thin core layer from the surfaceof the first clad after completion of the step of peeling the recessedmold.
 7. The method of manufacturing an optical waveguide, according toclaim 6, wherein the step of removing a thin core layer is performed byusing an oxygen-plasma process.
 8. The method of manufacturing anoptical waveguide, according to claim 1, wherein: the recessed mold has,at the ends of the recess, surface inclined at about 45° which areequivalent to inclined mirrors; and the core pattern has ends to whichthe surfaces equivalent to inclined mirrors have been transferred. 9.The method of manufacturing an optical waveguide, according to claim 8,further comprising a step of forming reflecting films on themirror-equivalent surfaces of the recessed mold before the step ofapplying a core material, wherein the step of peeling the recessed moldincludes a step of transferring the reflecting films to the ends of thecore pattern.
 10. The method of manufacturing an optical waveguide,according to claim 1, wherein: the recess of the recessed mold comprisestwo straight parts connected together, inclined at right angles to eachother, and surfaces equivalent to in-plane mirrors and designed toconnect the straight parts optically; and the core pattern has beenformed by transferring the straight parts and the surfaces equivalent toin-plane mirrors.
 11. The method of manufacturing an optical waveguide,according to claim 1, wherein the recess of the recessed mold hasconcave surfaces at ends.
 12. The method of manufacturing an opticalwaveguide, according to claim 1, wherein the recess of the recessed moldis shaped like a spacer and is deeper than the depth of core pattern.13. The method of manufacturing an optical waveguide, according to claim1, wherein the recess of the recessed mold is shaped like a base and isas deep as or deeper than the depth of core pattern.
 14. The method ofmanufacturing an optical waveguide, according to claim 1, wherein atleast a surface region of the recessed mold is made of silicone orfluororesin.
 15. The method of manufacturing an optical waveguide,according to claim 1, further comprising a step of performing a surfacetreatment on the recessed mold before the step of applying a corematerial, thereby to make the recessed mold has more affinity for thecore material.
 16. The method of manufacturing an optical waveguide,according to claim 15, wherein the surface treatment is an oxygen-plasmaprocess.
 17. The method of manufacturing an optical waveguide, accordingto claim 15, wherein the contact angle of the core material to therecessed mold is 45° or less.
 18. The method of manufacturing an opticalwaveguide, according to claim 1, further comprising: a step of forming aprojecting mold by providing a projection shaped like a core pattern, ona substrate; and a step of applying a resin to the projecting mold,curing the resin and peeling the projecting mold from the resin, therebyproviding a recessed mold.
 19. The method of manufacturing an opticalwaveguide, according to claim 18, wherein the projection of theprojecting mold comprises two straight parts connected together,inclined at right angles to each other, and surfaces equivalent toin-plane mirrors and designed to connect the straight parts optically.20. The method of manufacturing an optical waveguide, according to claim19, wherein the surfaces of the projection, which are equivalent toin-plane mirrors, are formed by a laser process.
 21. The method ofmanufacturing an optical waveguide, according to claim 19, wherein theprojection has surfaces at ends, which are equivalent to inclinedmirrors.
 22. The method of manufacturing an optical waveguide, accordingto claim 21, wherein the surfaces of the projection, which areequivalent to inclined mirrors, are inclined convex surfaces.
 23. Themethod of manufacturing an optical waveguide, according to claim 21,wherein the surfaces of the projection, which are equivalent to inclinedmirrors, are formed by a laser process.
 24. The method of manufacturingan optical waveguide, according to claim 22, wherein the step of forminga projecting mold further comprises: a step of forming a projection madeof a resist pattern and shaped like a core pattern, on the substrate bymeans of photolithography; a step of forming the inclined convexsurfaces by obliquely applying a laser beam to the ends of theprojection and thereby evaporating the ends of the projections in part,said laser beam defining a substantially circular shadow.
 25. The methodof manufacturing an optical waveguide, according to claim 22, whereinthe step of forming a projecting mold further comprises: a step offorming a projection made of a resist pattern and shaped like a corepattern, on the substrate by means of photolithography; and a step offorming the inclined convex surfaces by obliquely applying a laser beamto the ends of the projection a number of times, each time in adifferent direction, and thereby evaporating the ends of the projectionsin part.
 26. The method of manufacturing an optical waveguide, accordingto claim 22, wherein the step of forming a projecting mold furthercomprises: a step of forming a projection made of a resist pattern andshaped like a core pattern, on the substrate by means ofphotolithography; a step of forming inclined surface on the ends of theprojection by obliquely applying a laser beam to the ends of theprojection and thereby evaporating the ends of the projections in part;and a step of forming the inclined convex surfaces by raising atemperature after applying the laser beam, thereby causing the resist toflow.
 27. An optical waveguide having a plurality of cores interposedbetween clads, wherein the first core comprises a plurality of straightwaveguides extending in at least two directions and connected to eachother at an in-plane mirror, and another core comprises a straightwaveguide extending in a direction that is substantially identical toone of the directions in which the straight waveguides included in thefirst core extend.
 28. The optical waveguide according to claim 27,wherein an image of the in-plane mirror, projected on a plane extendingat right angles to a straight waveguide provided at an input side has awidth greater than a width of the core of the straight waveguideprovided at the input side.
 29. The optical waveguide according to claim28, wherein an image of the in-plane mirror, projected on a planeextending at right angles to a straight waveguide provided at an outputside has a width equal to or less than a width of the core of thestraight waveguide provided at the output side.
 30. The opticalwaveguide according to claim 27, wherein each of the cores has, at ends,inclined mirrors configured to connect the waveguide to externalelements.
 31. The optical waveguide according to claim 30, wherein theinclined mirrors have a width greater than a width of the core of thestraight waveguide which contacts the inclined mirror.
 32. The opticalwaveguide according to claim 31, wherein the inclined mirror having thewidth is formed on a light-output side.
 33. An optical waveguide inwhich a core is interposed between clads, comprising: a concave mirrorwhich is provided at one end of the core and which guides signal lightapplied in a direction perpendicular to the waveguide, into the core,wherein the concave mirror has a focal distance substantially equal to adistance from a center point of the concave mirror to a light-emittingpoint of a light-emitting element which generates the signal light. 34.An optical waveguide in which a core is interposed between clads,comprising: a concave mirror which is provided at one end of the coreand which guides signal light passing through the core in a directionperpendicular to the waveguide, wherein the concave mirror has a focaldistance ranging from ½ to unit of the distance between a center pointof the concave mirror and a light-receiving element provided on anoptical axis extending perpendicular to the waveguide.
 35. An opticalwaveguide which is to be bonded to another substrate, comprising: afirst clad; a core formed on a part of the first clad; and a spacerformed on a part of the first clad and having a top at a level higherthan the core.
 36. The optical waveguide according to claim 35, whereinthe spacer is made of the same material as the core.
 37. The opticalwaveguide according to claim 35, comprising: a second clad formed on thefirst clad covering the core; and another substrate bonded to the top ofthe spacer by using the second clad.
 38. The optical waveguide accordingto claim 37, wherein the substrate has a recess, and the spacer isfitted in the recess.
 39. An optical waveguide to be bonded to anothersubstrate, comprising: a first clad; a core formed on a part of thefirst clad; a base formed on a part of the first clad and having a topat a level equal to or higher than a top of the core; an alignment markformed on the top of the base; and a second clad formed on the firstclad and covering the core.
 40. The optical waveguide according to claim39, wherein the alignment mark is formed at a level equal to or higherthan the top of the core.
 41. The optical waveguide according to claim40, wherein: an optical-path changing mirror made of a metal film isprovided on an end of the core; and the alignment mark is a film made ofthe same metal as the optical-path changing mirror
 42. The opticalwaveguide according to claim 41, wherein the metal includes at least onemetal selected from the group consisting of Al, Au, Pt, Ag, Cu and Ti.43. The optical waveguide according to claim 39, comprising anothersubstrate which is bonded to the second clad and which has an alignmentmark formed at a position and opposing the alignment mark.